// Copyright 2014 The ql Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//MAYBE set operations
//MAYBE +=, -=, ...

//TODO verify there's a graceful failure for a 2G+ blob on a 32 bit machine.

// Package ql implements a pure Go embedded SQL database engine.
//
// QL is a member of the SQL family of languages. It is less complex and less
// powerful than SQL (whichever specification SQL is considered to be).
//
// Change list
//
// 2017-01-10: Release v1.1.0 fixes some bugs and adds a configurable WAL
// headroom.
//
//	https://github.com/cznic/ql/issues/140
//
// 2016-07-29: Release v1.0.6 enables alternatively using = instead of == for
// equality operation.
//
// 	https://github.com/cznic/ql/issues/131
//
// 2016-07-11: Release v1.0.5 undoes vendoring of lldb. QL now uses stable lldb
// (github.com/cznic/lldb).
//
// 	https://github.com/cznic/ql/issues/128
//
// 2016-07-06: Release v1.0.4 fixes a panic when closing the WAL file.
//
//	https://github.com/cznic/ql/pull/127
//
// 2016-04-03: Release v1.0.3 fixes a data race.
//
//	https://github.com/cznic/ql/issues/126
//
// 2016-03-23: Release v1.0.2 vendors github.com/cznic/exp/lldb and
// github.com/camlistore/go4/lock.
//
// 2016-03-17: Release v1.0.1 adjusts for latest goyacc. Parser error messages
// are improved and changed, but their exact form is not considered a API
// change.
//
// 2016-03-05: The current version has been tagged v1.0.0.
//
// 2015-06-15: To improve compatibility with other SQL implementations, the
// count built-in aggregate function now accepts * as its argument.
//
// 2015-05-29: The execution planner was rewritten from scratch. It should use
// indices in all places where they were used before plus in some additional
// situations.  It is possible to investigate the plan using the newly added
// EXPLAIN statement.  The QL tool is handy for such analysis. If the planner
// would have used an index, but no such exists, the plan includes hints in
// form of copy/paste ready CREATE INDEX statements.
//
// The planner is still quite simple and a lot of work on it is yet ahead. You
// can help this process by filling an issue with a schema and query which
// fails to use an index or indices when it should, in your opinion. Bonus
// points for including output of `ql 'explain <query>'`.
//
// 2015-05-09: The grammar of the CREATE INDEX statement now accepts an
// expression list instead of a single expression, which was further limited to
// just a column name or the built-in id().  As a side effect, composite
// indices are now functional. However, the values in the expression-list style
// index are not yet used by other statements or the statement/query planner.
// The composite index is useful while having UNIQUE clause to check for
// semantically duplicate rows before they get added to the table or when such
// a row is mutated using the UPDATE statement and the expression-list style
// index tuple of the row is thus recomputed.
//
// 2015-05-02: The Schema field of table __Table now correctly reflects any
// column constraints and/or defaults. Also, the (*DB).Info method now has that
// information provided in new ColumInfo fields NotNull, Constraint and
// Default.
//
// 2015-04-20: Added support for {LEFT,RIGHT,FULL} [OUTER] JOIN.
//
// 2015-04-18: Column definitions can now have constraints and defaults.
// Details are discussed in the "Constraints and defaults" chapter below the
// CREATE TABLE statement documentation.
//
// 2015-03-06: New built-in functions formatFloat and formatInt. Thanks
// urandom! (https://github.com/urandom)
//
// 2015-02-16: IN predicate now accepts a SELECT statement. See the updated
// "Predicates" section.
//
// 2015-01-17: Logical operators || and && have now alternative spellings: OR
// and AND (case insensitive).  AND was a keyword before, but OR is a new one.
// This can possibly break existing queries. For the record, it's a good idea
// to not use any name appearing in, for example, [7] in your queries as the
// list of QL's keywords may expand for gaining better compatibility with
// existing SQL "standards".
//
// 2015-01-12: ACID guarantees were tightened at the cost of performance in
// some cases. The write collecting window mechanism, a formerly used
// implementation detail, was removed. Inserting rows one by one in a
// transaction is now slow. I mean very slow. Try to avoid inserting single
// rows in a transaction. Instead, whenever possible, perform batch updates of
// tens to, say thousands of rows in a single transaction. See also:
// http://www.sqlite.org/faq.html#q19, the discussed synchronization principles
// involved are the same as for QL, modulo minor details.
//
// Note: A side effect is that closing a DB before exiting an application, both
// for the Go API and through database/sql driver, is no more required,
// strictly speaking. Beware that exiting an application while there is an open
// (uncommitted) transaction in progress means losing the transaction data.
// However, the DB will not become corrupted because of not closing it. Nor
// that was the case before, but formerly failing to close a DB could have
// resulted in losing the data of the last transaction.
//
// 2014-09-21: id() now optionally accepts a single argument - a table name.
//
// 2014-09-01: Added the DB.Flush() method and the LIKE pattern matching
// predicate.
//
// 2014-08-08: The built in functions max and min now accept also time values.
// Thanks opennota! (https://github.com/opennota)
//
// 2014-06-05: RecordSet interface extended by new methods FirstRow and Rows.
//
// 2014-06-02: Indices on id() are now used by SELECT statements.
//
// 2014-05-07: Introduction of Marshal, Schema, Unmarshal.
//
// 2014-04-15:
//
// Added optional IF NOT EXISTS clause to CREATE INDEX and optional IF EXISTS
// clause to DROP INDEX.
//
// 2014-04-12:
//
// The column Unique in the virtual table __Index was renamed to IsUnique
// because the old name is a keyword. Unfortunately, this is a breaking change,
// sorry.
//
// 2014-04-11: Introduction of LIMIT, OFFSET.
//
// 2014-04-10: Introduction of query rewriting.
//
// 2014-04-07: Introduction of indices.
//
// Building non CGO QL
//
// QL imports zappy[8], a block-based compressor, which speeds up its
// performance by using a C version of the compression/decompression
// algorithms.  If a CGO-free (pure Go) version of QL, or an app using QL, is
// required, please include 'purego' in the -tags option of go
// {build,get,install}. For example:
//
//	$ go get -tags purego github.com/cznic/ql
//
// If zappy was installed before installing QL, it might be necessary to
// rebuild zappy first (or rebuild QL with all its dependencies using the -a
// option):
//
//	$ touch "$GOPATH"/src/github.com/cznic/zappy/*.go
//	$ go install -tags purego github.com/cznic/zappy
//	$ go install github.com/cznic/ql
//
// Notation
//
// The syntax is specified using Extended Backus-Naur Form (EBNF)
//
// 	Production  = production_name "=" [ Expression ] "." .
// 	Expression  = Alternative { "|" Alternative } .
// 	Alternative = Term { Term } .
// 	Term        = production_name | token [ "…" token ] | Group | Option | Repetition .
// 	Group       = "(" Expression ")" .
// 	Option      = "[" Expression "]" .
// 	Repetition  = "{" Expression "}" .
// 	Productions are expressions constructed from terms and the following operators, in increasing precedence
//
// 	|   alternation
// 	()  grouping
// 	[]  option (0 or 1 times)
// 	{}  repetition (0 to n times)
//
// Lower-case production names are used to identify lexical tokens.
// Non-terminals are in CamelCase. Lexical tokens are enclosed in double quotes
// "" or back quotes ``.
//
// The form a … b represents the set of characters from a through b as
// alternatives. The horizontal ellipsis … is also used elsewhere in the spec
// to informally denote various enumerations or code snippets that are not
// further specified.
//
// QL source code representation
//
// QL source code is Unicode text encoded in UTF-8. The text is not
// canonicalized, so a single accented code point is distinct from the same
// character constructed from combining an accent and a letter; those are
// treated as two code points.  For simplicity, this document will use the
// unqualified term character to refer to a Unicode code point in the source
// text.
//
// Each code point is distinct; for instance, upper and lower case letters are
// different characters.
//
// Implementation restriction: For compatibility with other tools, the parser
// may disallow the NUL character (U+0000) in the statement.
//
// Implementation restriction: A byte order mark is disallowed anywhere in QL
// statements.
//
// Characters
//
// The following terms are used to denote specific character classes
//
//  newline        = . // the Unicode code point U+000A
//  unicode_char   = . // an arbitrary Unicode code point except newline
//  ascii_letter   = "a" … "z" | "A" … "Z" .
//
// Letters and digits
//
// The underscore character _ (U+005F) is considered a letter.
//
//  letter        = ascii_letter | "_" .
//  decimal_digit = "0" … "9" .
//  octal_digit   = "0" … "7" .
//  hex_digit     = "0" … "9" | "A" … "F" | "a" … "f" .
//
// Lexical elements
//
// Lexical elements are comments, tokens, identifiers, keywords, operators and
// delimiters, integer, floating-point, imaginary, rune and string literals and
// QL parameters.
//
// Comments
//
// There are three forms of comments
//
// Line comments start with the character sequence // or -- and stop at the end
// of the line. A line comment acts like a space.
//
// General comments start with the character sequence /* and continue through
// the character sequence */. A general comment acts like a space.
//
// Comments do not nest.
//
// Tokens
//
// Tokens form the vocabulary of QL. There are four classes: identifiers,
// keywords, operators and delimiters, and literals. White space, formed from
// spaces (U+0020), horizontal tabs (U+0009), carriage returns (U+000D), and
// newlines (U+000A), is ignored except as it separates tokens that would
// otherwise combine into a single token.
//
// Semicolons
//
// The formal grammar uses semicolons ";" as separators of QL statements. A
// single QL statement or the last QL statement in a list of statements can
// have an optional semicolon terminator. (Actually a separator from the
// following empty statement.)
//
// Identifiers
//
// Identifiers name entities such as tables or record set columns. An
// identifier is a sequence of one or more letters and digits. The first
// character in an identifier must be a letter.
//
//  identifier = letter { letter | decimal_digit } .
//
// For example
//
// 	price
// 	_tmp42
// 	Sales
//
// No identifiers are predeclared, however note that no keyword can be used as
// an identifier.  Identifiers starting with two underscores are used for meta
// data virtual tables names. For forward compatibility, users should generally
// avoid using any identifiers starting with two underscores. For example
//
//	__Column
//	__Column2
//	__Index
//	__Table
//
// Keywords
//
// The following keywords are reserved and may not be used as identifiers.
//
//	ADD	      complex128    FROM	  LEFT		string
//	ALTER	      complex64	    FULL	  LIKE		TABLE
//	AND	      CREATE	    GROUP	  LIMIT		time
//	AS	      DEFAULT	    IF		  NOT		TRANSACTION
//	ASC	      DELETE	    IN		  NULL		true
//	BEGIN	      DESC	    INDEX	  OFFSET	TRUNCATE
//	BETWEEN	      DISTINCT	    INSERT	  ON		uint
//	bigint	      DROP	    int		  OR		uint16
//	bigrat	      duration	    int16	  ORDER		uint32
//	blob	      EXISTS	    int32	  OUTER		uint64
//	bool	      EXPLAIN	    int64	  RIGHT		uint8
//	BY	      false	    int8	  ROLLBACK	UNIQUE
//	byte	      float	    INTO	  rune		UPDATE
//	COLUMN	      float32	    IS		  SELECT	VALUES
//	COMMIT	      float64	    JOIN	  SET		WHERE
//
// Keywords are not case sensitive.
//
// Operators and Delimiters
//
// The following character sequences represent operators, delimiters, and other
// special tokens
//
// 	+    &    &&    ==    !=    (    )
// 	-    |    ||    <     <=    [    ]
// 	*    ^          >     >=    ,    ;
// 	/    <<         =           .
// 	%    >>         !
// 	     &^
//
// Operators consisting of more than one character are referred to by names in
// the rest of the documentation
//
//  andand = "&&" .
//  andnot = "&^" .
//  lsh    = "<<" .
//  le     = "<=" .
//  eq     = "==" | "=" .
//  ge     = ">=" .
//  neq    = "!=" .
//  oror   = "||" .
//  rsh    = ">>" .
//
// Integer literals
//
// An integer literal is a sequence of digits representing an integer constant.
// An optional prefix sets a non-decimal base: 0 for octal, 0x or 0X for
// hexadecimal.  In hexadecimal literals, letters a-f and A-F represent values
// 10 through 15.
//
//  int_lit     = decimal_lit | octal_lit | hex_lit .
//  decimal_lit = ( "1" … "9" ) { decimal_digit } .
//  octal_lit   = "0" { octal_digit } .
//  hex_lit     = "0" ( "x" | "X" ) hex_digit { hex_digit } .
//
// For example
//
// 	42
// 	0600
// 	0xBadFace
// 	1701411834604692
//
// Floating-point literals
//
// A floating-point literal is a decimal representation of a floating-point
// constant. It has an integer part, a decimal point, a fractional part, and an
// exponent part. The integer and fractional part comprise decimal digits; the
// exponent part is an e or E followed by an optionally signed decimal
// exponent.  One of the integer part or the fractional part may be elided; one
// of the decimal point or the exponent may be elided.
//
//  float_lit = decimals "." [ decimals ] [ exponent ] |
//              decimals exponent |
//              "." decimals [ exponent ] .
//  decimals  = decimal_digit { decimal_digit } .
//  exponent  = ( "e" | "E" ) [ "+" | "-" ] decimals .
//
// For example
//
// 	0.
// 	72.40
// 	072.40  // == 72.40
// 	2.71828
// 	1.e+0
// 	6.67428e-11
// 	1E6
// 	.25
// 	.12345E+5
//
// Imaginary literals
//
// An imaginary literal is a decimal representation of the imaginary part of a
// complex constant. It consists of a floating-point literal or decimal integer
// followed by the lower-case letter i.
//
//  imaginary_lit = (decimals | float_lit) "i" .
//
// For example
//
// 	0i
// 	011i  // == 11i
// 	0.i
// 	2.71828i
// 	1.e+0i
// 	6.67428e-11i
// 	1E6i
// 	.25i
// 	.12345E+5i
//
// Rune literals
//
// A rune literal represents a rune constant, an integer value identifying a
// Unicode code point. A rune literal is expressed as one or more characters
// enclosed in single quotes. Within the quotes, any character may appear
// except single quote and newline. A single quoted character represents the
// Unicode value of the character itself, while multi-character sequences
// beginning with a backslash encode values in various formats.
//
// The simplest form represents the single character within the quotes; since
// QL statements are Unicode characters encoded in UTF-8, multiple
// UTF-8-encoded bytes may represent a single integer value. For instance, the
// literal 'a' holds a single byte representing a literal a, Unicode U+0061,
// value 0x61, while 'ä' holds two bytes (0xc3 0xa4) representing a literal
// a-dieresis, U+00E4, value 0xe4.
//
// Several backslash escapes allow arbitrary values to be encoded as ASCII
// text.  There are four ways to represent the integer value as a numeric
// constant: \x followed by exactly two hexadecimal digits; \u followed by
// exactly four hexadecimal digits; \U followed by exactly eight hexadecimal
// digits, and a plain backslash \ followed by exactly three octal digits. In
// each case the value of the literal is the value represented by the digits in
// the corresponding base.
//
// Although these representations all result in an integer, they have different
// valid ranges. Octal escapes must represent a value between 0 and 255
// inclusive.  Hexadecimal escapes satisfy this condition by construction. The
// escapes \u and \U represent Unicode code points so within them some values
// are illegal, in particular those above 0x10FFFF and surrogate halves.
//
// After a backslash, certain single-character escapes represent special
// values
//
// 	\a   U+0007 alert or bell
// 	\b   U+0008 backspace
// 	\f   U+000C form feed
// 	\n   U+000A line feed or newline
// 	\r   U+000D carriage return
// 	\t   U+0009 horizontal tab
// 	\v   U+000b vertical tab
// 	\\   U+005c backslash
// 	\'   U+0027 single quote  (valid escape only within rune literals)
// 	\"   U+0022 double quote  (valid escape only within string literals)
//
// All other sequences starting with a backslash are illegal inside rune
// literals.
//
//  rune_lit         = "'" ( unicode_value | byte_value ) "'" .
//  unicode_value    = unicode_char | little_u_value | big_u_value | escaped_char .
//  byte_value       = octal_byte_value | hex_byte_value .
//  octal_byte_value = `\` octal_digit octal_digit octal_digit .
//  hex_byte_value   = `\` "x" hex_digit hex_digit .
//  little_u_value   = `\` "u" hex_digit hex_digit hex_digit hex_digit .
//  big_u_value      = `\` "U" hex_digit hex_digit hex_digit hex_digit
//                             hex_digit hex_digit hex_digit hex_digit .
//  escaped_char     = `\` ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .
//
// For example
//
// 	'a'
// 	'ä'
// 	'本'
// 	'\t'
// 	'\000'
// 	'\007'
// 	'\377'
// 	'\x07'
// 	'\xff'
// 	'\u12e4'
// 	'\U00101234'
// 	'aa'         // illegal: too many characters
// 	'\xa'        // illegal: too few hexadecimal digits
// 	'\0'         // illegal: too few octal digits
// 	'\uDFFF'     // illegal: surrogate half
// 	'\U00110000' // illegal: invalid Unicode code point
//
// String literals
//
// A string literal represents a string constant obtained from concatenating a
// sequence of characters. There are two forms: raw string literals and
// interpreted string literals.
//
// Raw string literals are character sequences between back quotes ``. Within
// the quotes, any character is legal except back quote. The value of a raw
// string literal is the string composed of the uninterpreted (implicitly
// UTF-8-encoded) characters between the quotes; in particular, backslashes
// have no special meaning and the string may contain newlines. Carriage
// returns inside raw string literals are discarded from the raw string value.
//
// Interpreted string literals are character sequences between double quotes
// "".  The text between the quotes, which may not contain newlines, forms the
// value of the literal, with backslash escapes interpreted as they are in rune
// literals (except that \' is illegal and \" is legal), with the same
// restrictions. The three-digit octal (\nnn) and two-digit hexadecimal (\xnn)
// escapes represent individual bytes of the resulting string; all other
// escapes represent the (possibly multi-byte) UTF-8 encoding of individual
// characters. Thus inside a string literal \377 and \xFF represent a single
// byte of value 0xFF=255, while ÿ, \u00FF, \U000000FF and \xc3\xbf represent
// the two bytes 0xc3 0xbf of the UTF-8 encoding of character U+00FF.
//
//  string_lit             = raw_string_lit | interpreted_string_lit .
//  raw_string_lit         = "`" { unicode_char | newline } "`" .
//  interpreted_string_lit = `"` { unicode_value | byte_value } `"` .
//
// For example
//
// 	`abc`  // same as "abc"
// 	`\n
// 	\n`    // same as "\\n\n\\n"
// 	"\n"
// 	""
// 	"Hello, world!\n"
// 	"日本語"
// 	"\u65e5本\U00008a9e"
// 	"\xff\u00FF"
// 	"\uD800"       // illegal: surrogate half
// 	"\U00110000"   // illegal: invalid Unicode code point
//
// These examples all represent the same string
//
// 	"日本語"                                 // UTF-8 input text
// 	`日本語`                                 // UTF-8 input text as a raw literal
// 	"\u65e5\u672c\u8a9e"                    // the explicit Unicode code points
// 	"\U000065e5\U0000672c\U00008a9e"        // the explicit Unicode code points
// 	"\xe6\x97\xa5\xe6\x9c\xac\xe8\xaa\x9e"  // the explicit UTF-8 bytes
//
// If the statement source represents a character as two code points, such as a
// combining form involving an accent and a letter, the result will be an error
// if placed in a rune literal (it is not a single code point), and will appear
// as two code points if placed in a string literal.
//
// QL parameters
//
// Literals are assigned their values from the respective text representation
// at "compile" (parse) time. QL parameters provide the same functionality as
// literals, but their value is assigned at execution time from an expression
// list passed to DB.Run or DB.Execute. Using '?' or '$' is completely
// equivalent.
//
//  ql_parameter = ( "?" | "$" ) "1" … "9" { "0" … "9" } .
//
// For example
//
// 	SELECT DepartmentID
// 	FROM department
// 	WHERE DepartmentID == ?1
// 	ORDER BY DepartmentName;
//
// 	SELECT employee.LastName
// 	FROM department, employee
// 	WHERE department.DepartmentID == $1 && employee.LastName > $2
// 	ORDER BY DepartmentID;
//
// Constants
//
// Keywords 'false' and 'true' (not case sensitive) represent the two possible
// constant values of type bool (also not case sensitive).
//
// Keyword 'NULL' (not case sensitive) represents an untyped constant which is
// assignable to any type. NULL is distinct from any other value of any type.
//
// Types
//
// A type determines the set of values and operations specific to values of
// that type. A type is specified by a type name.
//
//  Type = "bigint"      // http://golang.org/pkg/math/big/#Int
//       | "bigrat"      // http://golang.org/pkg/math/big/#Rat
//       | "blob"        // []byte
//       | "bool"
//       | "byte"        // alias for uint8
//       | "complex128"
//       | "complex64"
//       | "duration"    // http://golang.org/pkg/time/#Duration
//       | "float"       // alias for float64
//       | "float32"
//       | "float64"
//       | "int"         // alias for int64
//       | "int16"
//       | "int32"
//       | "int64"
//       | "int8"
//       | "rune"        // alias for int32
//       | "string"
//       | "time"        // http://golang.org/pkg/time/#Time
//       | "uint"        // alias for uint64
//       | "uint16"
//       | "uint32"
//       | "uint64"
//       | "uint8" .
//
// Named instances of the boolean, numeric, and string types are keywords. The
// names are not case sensitive.
//
// Note: The blob type is exchanged between the back end and the API as []byte.
// On 32 bit platforms this limits the size which the implementation can handle
// to 2G.
//
// Boolean types
//
// A boolean type represents the set of Boolean truth values denoted by the
// predeclared constants true and false. The predeclared boolean type is bool.
//
// Duration type
//
// A duration type represents the elapsed time between two instants as an int64
// nanosecond count. The representation limits the largest representable
// duration to approximately 290 years.
//
// Numeric types
//
// A numeric type represents sets of integer or floating-point values. The
// predeclared architecture-independent numeric types are
//
// 	uint8       the set of all unsigned  8-bit integers (0 to 255)
// 	uint16      the set of all unsigned 16-bit integers (0 to 65535)
// 	uint32      the set of all unsigned 32-bit integers (0 to 4294967295)
// 	uint64      the set of all unsigned 64-bit integers (0 to 18446744073709551615)
//
// 	int8        the set of all signed  8-bit integers (-128 to 127)
// 	int16       the set of all signed 16-bit integers (-32768 to 32767)
// 	int32       the set of all signed 32-bit integers (-2147483648 to 2147483647)
// 	int64       the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807)
// 	duration    the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807)
//	bigint      the set of all integers
//
//	bigrat      the set of all rational numbers
//
// 	float32     the set of all IEEE-754 32-bit floating-point numbers
// 	float64     the set of all IEEE-754 64-bit floating-point numbers
//
// 	complex64   the set of all complex numbers with float32 real and imaginary parts
// 	complex128  the set of all complex numbers with float64 real and imaginary parts
//
// 	byte        alias for uint8
// 	float       alias for float64
// 	int         alias for int64
// 	rune        alias for int32
// 	uint        alias for uint64
//
// The value of an n-bit integer is n bits wide and represented using two's
// complement arithmetic.
//
// Conversions are required when different numeric types are mixed in an
// expression or assignment.
//
// String types
//
// A string type represents the set of string values. A string value is a
// (possibly empty) sequence of bytes. The case insensitive keyword for the
// string type is 'string'.
//
// The length of a string (its size in bytes) can be discovered using the
// built-in function len.
//
// Time types
//
// A time type represents an instant in time with nanosecond precision. Each
// time has associated with it a location, consulted when computing the
// presentation form of the time.
//
// Predeclared functions
//
// The following functions are implicitly declared
//
//	avg          complex     contains    count       date
//	day          formatTime  formatFloat formatInt
//	hasPrefix    hasSuffix   hour        hours       id
//	imag         len         max         min         minute
//	minutes      month       nanosecond  nanoseconds now
//	parseTime    real        second      seconds     since
//	sum          timeIn      weekday     year        yearDay
//
// Expressions
//
// An expression specifies the computation of a value by applying operators and
// functions to operands.
//
// Operands
//
// Operands denote the elementary values in an expression. An operand may be a
// literal, a (possibly qualified) identifier denoting a constant or a function
// or a table/record set column, or a parenthesized expression.
//
//  Operand = Literal | QualifiedIdent | "(" Expression ")" .
//  Literal = "FALSE" | "NULL" | "TRUE"
//  	| float_lit | imaginary_lit | int_lit | rune_lit | string_lit
//  	| ql_parameter .
//
// Qualified identifiers
//
// A qualified identifier is an identifier qualified with a table/record set
// name prefix.
//
//  QualifiedIdent = identifier [ "." identifier ] .
//
// For example
//
// 	invoice.Num	// might denote column 'Num' from table 'invoice'
//
// Primary expressions
//
// Primary expression are the operands for unary and binary expressions.
//
//  PrimaryExpression = Operand
//              | Conversion
//              | PrimaryExpression Index
//              | PrimaryExpression Slice
//              | PrimaryExpression Call .
//
//  Call  = "(" [ "*" | ExpressionList ] ")" . // * only in count(*).
//  Index = "[" Expression "]" .
//  Slice = "[" [ Expression ] ":" [ Expression ] "]" .
//
// For example
//
// 	x
// 	2
// 	(s + ".txt")
// 	f(3.1415, true)
// 	s[i : j + 1]
//
// Index expressions
//
// A primary expression of the form
//
// 	s[x]
//
// denotes the element of a string indexed by x. Its type is byte. The value x
// is called the index.  The following rules apply
//
// - The index x must be of integer type except bigint or duration; it is in
// range if 0 <= x < len(s), otherwise it is out of range.
//
// - A constant index must be non-negative and representable by a value of type
// int.
//
// - A constant index must be in range if the string a is a literal.
//
// - If x is out of range at run time, a run-time error occurs.
//
// - s[x] is the byte at index x and the type of s[x] is byte.
//
// If s is NULL or x is NULL then the result is NULL.
//
// Otherwise s[x] is illegal.
//
// Slices
//
// For a string, the primary expression
//
// 	s[low : high]
//
// constructs a substring. The indices low and high select which elements
// appear in the result. The result has indices starting at 0 and length equal
// to high - low.
//
// For convenience, any of the indices may be omitted. A missing low index
// defaults to zero; a missing high index defaults to the length of the sliced
// operand
//
// 	s[2:]  // same s[2 : len(s)]
// 	s[:3]  // same as s[0 : 3]
// 	s[:]   // same as s[0 : len(s)]
//
// The indices low and high are in range if 0 <= low <= high <= len(a),
// otherwise they are out of range. A constant index must be non-negative and
// representable by a value of type int. If both indices are constant, they
// must satisfy low <= high. If the indices are out of range at run time, a
// run-time error occurs.
//
// Integer values of type bigint or duration cannot be used as indices.
//
// If s is NULL the result is NULL. If low or high is not omitted and is NULL
// then the result is NULL.
//
// Calls
//
// Given an identifier f denoting a predeclared function,
//
// 	f(a1, a2, … an)
//
// calls f with arguments a1, a2, … an. Arguments are evaluated before the
// function is called. The type of the expression is the result type of f.
//
// 	complex(x, y)
// 	len(name)
//
// In a function call, the function value and arguments are evaluated in the
// usual order. After they are evaluated, the parameters of the call are passed
// by value to the function and the called function begins execution. The
// return value of the function is passed by value when the function returns.
//
// Calling an undefined function causes a compile-time error.
//
// Operators
//
// Operators combine operands into expressions.
//
//  Expression = Term { ( oror | "OR" ) Term } .
//
//  ExpressionList = Expression { "," Expression } [ "," ].
//  Factor =  PrimaryFactor  { ( ge | ">" | le | "<" | neq | eq | "LIKE" ) PrimaryFactor } [ Predicate ] .
//  PrimaryFactor = PrimaryTerm  { ( "^" | "|" | "-" | "+" ) PrimaryTerm } .
//  PrimaryTerm = UnaryExpr { ( andnot | "&" | lsh | rsh | "%" | "/" | "*" ) UnaryExpr } .
//  Term = Factor { ( andand | "AND" ) Factor } .
//  UnaryExpr = [ "^" | "!" | "-" | "+" ] PrimaryExpression .
//
// Comparisons are discussed elsewhere. For other binary operators, the operand
// types must be identical unless the operation involves shifts or untyped
// constants. For operations involving constants only, see the section on
// constant expressions.
//
// Except for shift operations, if one operand is an untyped constant and the
// other operand is not, the constant is converted to the type of the other
// operand.
//
// The right operand in a shift expression must have unsigned integer type or
// be an untyped constant that can be converted to unsigned integer type. If
// the left operand of a non-constant shift expression is an untyped constant,
// the type of the constant is what it would be if the shift expression were
// replaced by its left operand alone.
//
// Pattern matching
//
// Expressions of the form
//
//	expr1 LIKE expr2
//
// yield a boolean value true if expr2, a regular expression, matches expr1
// (see also [6]).  Both expression must be of type string. If any one of the
// expressions is NULL the result is NULL.
//
// Predicates
//
// Predicates are special form expressions having a boolean result type.
//
// Expressions of the form
//
//	expr IN ( expr1, expr2, expr3, ... )		// case A
//
//	expr NOT IN ( expr1, expr2, expr3, ... )	// case B
//
// are equivalent, including NULL handling, to
//
//	expr == expr1 || expr == expr2 || expr == expr3 || ...	// case A
//
//	expr != expr1 && expr != expr2 && expr != expr3 && ...	// case B
//
// The types of involved expressions must be comparable as defined in
// "Comparison operators".
//
// Another form of the IN predicate creates the expression list from a result
// of a SelectStmt.
//
//	DELETE FROM t WHERE id() IN (SELECT id_t FROM u WHERE inactive_days > 365)
//
// The SelectStmt must select only one column. The produced expression list is
// resource limited by the memory available to the process. NULL values
// produced by the SelectStmt are ignored, but if all records of the SelectStmt
// are NULL the predicate yields NULL. The select statement is evaluated only
// once. If the type of expr is not the same as the type of the field returned
// by the SelectStmt then the set operation yields false. The type of the
// column returned by the SelectStmt must be one of the simple (non blob-like)
// types:
//
//	bool
//	byte         // alias uint8
//	complex128
//	complex64
//	float        // alias float64
//	float32
//	float64
//	int          // alias int64
//	int16
//	int32
//	int64
//	int8
//	rune         // alias int32
//	string
//	uint         // alias uint64
//	uint16
//	uint32
//	uint64
//	uint8
//
// Expressions of the form
//
//	expr BETWEEN low AND high	// case A
//
//	expr NOT BETWEEN low AND high	// case B
//
// are equivalent, including NULL handling, to
//
//	expr >= low && expr <= high	// case A
//
//	expr < low || expr > high	// case B
//
// The types of involved expressions must be ordered as defined in "Comparison
// operators".
//
//  Predicate = (
//  			[ "NOT" ] (
//  			  "IN" "(" ExpressionList ")"
//  			| "IN" "(" SelectStmt [ ";" ] ")"
//  			| "BETWEEN" PrimaryFactor "AND" PrimaryFactor
//  			)
//              |       "IS" [ "NOT" ] "NULL"
//  	).
//
// Expressions of the form
//
//	expr IS NULL		// case A
//
//	expr IS NOT NULL	// case B
//
// yield a boolean value true if expr does not have a specific type (case A) or
// if expr has a specific type (case B). In other cases the result is a boolean
// value false.
//
// Operator precedence
//
// Unary operators have the highest precedence.
//
// There are five precedence levels for binary operators. Multiplication
// operators bind strongest, followed by addition operators, comparison
// operators, && (logical AND), and finally || (logical OR)
//
// 	Precedence    Operator
// 	    5             *  /  %  <<  >>  &  &^
// 	    4             +  -  |  ^
// 	    3             ==  !=  <  <=  >  >=
// 	    2             &&
// 	    1             ||
//
// Binary operators of the same precedence associate from left to right. For
// instance, x / y * z is the same as (x / y) * z.
//
// 	+x
// 	23 + 3*x[i]
// 	x <= f()
// 	^a >> b
// 	f() || g()
// 	x == y+1 && z > 0
//
// Note that the operator precedence is reflected explicitly by the grammar.
//
// Arithmetic operators
//
// Arithmetic operators apply to numeric values and yield a result of the same
// type as the first operand. The four standard arithmetic operators (+, -, *,
// /) apply to integer, rational, floating-point, and complex types; + also
// applies to strings; +,- also applies to times.  All other arithmetic
// operators apply to integers only.
//
// 	+    sum                    integers, rationals, floats, complex values, strings
// 	-    difference             integers, rationals, floats, complex values, times
// 	*    product                integers, rationals, floats, complex values
// 	/    quotient               integers, rationals, floats, complex values
// 	%    remainder              integers
//
// 	&    bitwise AND            integers
// 	|    bitwise OR             integers
// 	^    bitwise XOR            integers
// 	&^   bit clear (AND NOT)    integers
//
// 	<<   left shift             integer << unsigned integer
// 	>>   right shift            integer >> unsigned integer
//
// Strings can be concatenated using the + operator
//
// 	"hi" + string(c) + " and good bye"
//
// String addition creates a new string by concatenating the operands.
//
// A value of type duration can be added to or subtracted from a value of type time.
//
//	now() + duration("1h")	// time after 1 hour from now
//	duration("1h") + now()	// time after 1 hour from now
//	now() - duration("1h")	// time before 1 hour from now
//	duration("1h") - now()	// illegal, negative times do not exist
//
// Times can subtracted from each other producing a value of type duration.
//
//	now() - t0	// elapsed time since t0
//	now() + now()	// illegal, operator + not defined for times
//
// For two integer values x and y, the integer quotient q = x / y and remainder
// r = x % y satisfy the following relationships
//
// 	x = q*y + r  and  |r| < |y|
//
// with x / y truncated towards zero ("truncated division").
//
// 	 x     y     x / y     x % y
// 	 5     3       1         2
// 	-5     3      -1        -2
// 	 5    -3      -1         2
// 	-5    -3       1        -2
//
// As an exception to this rule, if the dividend x is the most negative value
// for the int type of x, the quotient q = x / -1 is equal to x (and r = 0).
//
// 				 x, q
// 	int8                     -128
// 	int16                  -32768
// 	int32             -2147483648
// 	int64    -9223372036854775808
//
// If the divisor is a constant expression, it must not be zero. If the divisor
// is zero at run time, a run-time error occurs. If the dividend is
// non-negative and the divisor is a constant power of 2, the division may be
// replaced by a right shift, and computing the remainder may be replaced by a
// bitwise AND operation
//
// 	 x     x / 4     x % 4     x >> 2     x & 3
// 	 11      2         3         2          3
// 	-11     -2        -3        -3          1
//
// The shift operators shift the left operand by the shift count specified by
// the right operand. They implement arithmetic shifts if the left operand is a
// signed integer and logical shifts if it is an unsigned integer. There is no
// upper limit on the shift count. Shifts behave as if the left operand is
// shifted n times by 1 for a shift count of n. As a result, x << 1 is the same
// as x*2 and x >> 1 is the same as x/2 but truncated towards negative
// infinity.
//
// For integer operands, the unary operators +, -, and ^ are defined as follows
//
// 	+x                          is 0 + x
// 	-x    negation              is 0 - x
// 	^x    bitwise complement    is m ^ x  with m = "all bits set to 1" for unsigned x
// 	                                      and  m = -1 for signed x
//
// For floating-point and complex numbers, +x is the same as x, while -x is the
// negation of x. The result of a floating-point or complex division by zero is
// not specified beyond the IEEE-754 standard; whether a run-time error occurs
// is implementation-specific.
//
// Whenever any operand of any arithmetic operation, unary or binary, is NULL,
// as well as in the case of the string concatenating operation, the result is
// NULL.
//
//	42*NULL		// the result is NULL
//	NULL/x		// the result is NULL
//	"foo"+NULL	// the result is NULL
//
// Integer overflow
//
// For unsigned integer values, the operations +, -, *, and << are computed
// modulo 2n, where n is the bit width of the unsigned integer's type. Loosely
// speaking, these unsigned integer operations discard high bits upon overflow,
// and expressions may rely on ``wrap around''.
//
// For signed integers with a finite bit width, the operations +, -, *, and <<
// may legally overflow and the resulting value exists and is deterministically
// defined by the signed integer representation, the operation, and its
// operands. No exception is raised as a result of overflow. An evaluator may
// not optimize an expression under the assumption that overflow does not
// occur. For instance, it may not assume that x < x + 1 is always true.
//
// Integers of type bigint and rationals do not overflow but their handling is
// limited by the memory resources available to the program.
//
// Comparison operators
//
// Comparison operators compare two operands and yield a boolean value.
//
// 	==    equal
// 	!=    not equal
// 	<     less
// 	<=    less or equal
// 	>     greater
// 	>=    greater or equal
//
// In any comparison, the first operand must be of same type as is the second
// operand, or vice versa.
//
// The equality operators == and != apply to operands that are comparable. The
// ordering operators <, <=, >, and >= apply to operands that are ordered.
// These terms and the result of the comparisons are defined as follows
//
// - Boolean values are comparable. Two boolean values are equal if they are
// either both true or both false.
//
// - Complex values are comparable. Two complex values u and v are equal if
// both real(u) == real(v) and imag(u) == imag(v).
//
// - Integer values are comparable and ordered, in the usual way. Note that
// durations are integers.
//
// - Floating point values are comparable and ordered, as defined by the
// IEEE-754 standard.
//
// - Rational values are comparable and ordered, in the usual way.
//
// - String values are comparable and ordered, lexically byte-wise.
//
// - Time values are comparable and ordered.
//
// Whenever any operand of any comparison operation is NULL, the result is
// NULL.
//
// Note that slices are always of type string.
//
// Logical operators
//
// Logical operators apply to boolean values and yield a boolean result. The
// right operand is evaluated conditionally.
//
// 	&&    conditional AND    p && q  is  "if p then q else false"
// 	||    conditional OR     p || q  is  "if p then true else q"
// 	!     NOT                !p      is  "not p"
//
// The truth tables for logical operations with NULL values
//
// 	+-------+-------+---------+---------+
// 	|   p   |   q   |  p || q |  p && q |
// 	+-------+-------+---------+---------+
// 	| true  | true  | *true   |  true   |
// 	| true  | false | *true   |  false  |
// 	| true  | NULL  | *true   |  NULL   |
// 	| false | true  |  true   | *false  |
// 	| false | false |  false  | *false  |
// 	| false | NULL  |  NULL   | *false  |
// 	| NULL  | true  |  true   |  NULL   |
// 	| NULL  | false |  NULL   |  false  |
// 	| NULL  | NULL  |  NULL   |  NULL   |
// 	+-------+-------+---------+---------+
// 	 * indicates q is not evaluated.
//
// 	+-------+-------+
// 	|   p   |  !p   |
// 	+-------+-------+
// 	| true  | false |
// 	| false | true  |
// 	| NULL  | NULL  |
// 	+-------+-------+
//
// Conversions
//
// Conversions are expressions of the form T(x) where T is a type and x is an
// expression that can be converted to type T.
//
//  Conversion = Type "(" Expression ")" .
//
// A constant value x can be converted to type T in any of these cases:
//
// - x is representable by a value of type T.
//
// - x is a floating-point constant, T is a floating-point type, and x is
// representable by a value of type T after rounding using IEEE 754
// round-to-even rules. The constant T(x) is the rounded value.
//
// - x is an integer constant and T is a string type. The same rule as for
// non-constant x applies in this case.
//
// Converting a constant yields a typed constant as result.
//
// 	float32(2.718281828)     // 2.718281828 of type float32
// 	complex128(1)            // 1.0 + 0.0i of type complex128
// 	float32(0.49999999)      // 0.5 of type float32
// 	string('x')              // "x" of type string
// 	string(0x266c)           // "♬" of type string
// 	"foo" + "bar"            // "foobar"
// 	int(1.2)                 // illegal: 1.2 cannot be represented as an int
// 	string(65.0)             // illegal: 65.0 is not an integer constant
//
// A non-constant value x can be converted to type T in any of these cases:
//
// - x has type T.
//
// - x's type and T are both integer or floating point types.
//
// - x's type and T are both complex types.
//
// - x is an integer, except bigint or duration, and T is a string type.
//
// Specific rules apply to (non-constant) conversions between numeric types or
// to and from a string type. These conversions may change the representation
// of x and incur a run-time cost. All other conversions only change the type
// but not the representation of x.
//
// A conversion of NULL to any type yields NULL.
//
// Conversions between numeric types
//
// For the conversion of non-constant numeric values, the following rules
// apply
//
// 1. When converting between integer types, if the value is a signed integer,
// it is sign extended to implicit infinite precision; otherwise it is zero
// extended.  It is then truncated to fit in the result type's size. For
// example, if v == uint16(0x10F0), then uint32(int8(v)) == 0xFFFFFFF0. The
// conversion always yields a valid value; there is no indication of overflow.
//
// 2. When converting a floating-point number to an integer, the fraction is
// discarded (truncation towards zero).
//
// 3. When converting an integer or floating-point number to a floating-point
// type, or a complex number to another complex type, the result value is
// rounded to the precision specified by the destination type. For instance,
// the value of a variable x of type float32 may be stored using additional
// precision beyond that of an IEEE-754 32-bit number, but float32(x)
// represents the result of rounding x's value to 32-bit precision. Similarly,
// x + 0.1 may use more than 32 bits of precision, but float32(x + 0.1) does
// not.
//
// In all non-constant conversions involving floating-point or complex values,
// if the result type cannot represent the value the conversion succeeds but
// the result value is implementation-dependent.
//
// Conversions to and from a string type
//
// 1. Converting a signed or unsigned integer value to a string type yields a
// string containing the UTF-8 representation of the integer. Values outside
// the range of valid Unicode code points are converted to "\uFFFD".
//
// 	string('a')       // "a"
// 	string(-1)        // "\ufffd" == "\xef\xbf\xbd"
// 	string(0xf8)      // "\u00f8" == "ø" == "\xc3\xb8"
// 	string(0x65e5)    // "\u65e5" == "日" == "\xe6\x97\xa5"
//
// 2. Converting a blob to a string type yields a string whose successive bytes
// are the elements of the blob.
//
//	string(b /* []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'} */)   // "hellø"
//	string(b /* []byte{} */)                                     // ""
//	string(b /* []byte(nil) */)                                  // ""
//
// 3. Converting a value of a string type to a blob yields a blob whose
// successive elements are the bytes of the string.
//
//	blob("hellø")   // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
//	blob("")        // []byte{}
//
// 4. Converting a value of a bigint type to a string yields a string
// containing the decimal decimal representation of the integer.
//
//	string(M9)	// "2305843009213693951"
//
// 5. Converting a value of a string type to a bigint yields a bigint value
// containing the integer represented by the string value. A prefix of “0x” or
// “0X” selects base 16; the “0” prefix selects base 8, and a “0b” or “0B”
// prefix selects base 2. Otherwise the value is interpreted in base 10. An
// error occurs if the string value is not in any valid format.
//
//	bigint("2305843009213693951")		// M9
//	bigint("0x1ffffffffffffffffffffff")	// M10 == 2^89-1
//
// 6. Converting a value of a rational type to a string yields a string
// containing the decimal decimal representation of the rational in the form
// "a/b" (even if b == 1).
//
//	string(bigrat(355)/bigrat(113))	// "355/113"
//
// 7. Converting a value of a string type to a bigrat yields a bigrat value
// containing the rational represented by the string value. The string can be
// given as a fraction "a/b" or as a floating-point number optionally followed
// by an exponent. An error occurs if the string value is not in any valid
// format.
//
//	bigrat("1.2e-34")
//	bigrat("355/113")
//
// 8. Converting a value of a duration type to a string returns a string
// representing the duration in the form "72h3m0.5s". Leading zero units are
// omitted. As a special case, durations less than one second format using a
// smaller unit (milli-, micro-, or nanoseconds) to ensure that the leading
// digit is non-zero. The zero duration formats as 0, with no unit.
//
//	string(elapsed)	// "1h", for example
//
// 9. Converting a string value to a duration yields a duration represented by
// the string.  A duration string is a possibly signed sequence of decimal
// numbers, each with optional fraction and a unit suffix, such as "300ms",
// "-1.5h" or "2h45m". Valid time units are "ns", "us" (or "µs"), "ms", "s",
// "m", "h".
//
//	duration("1m")	// http://golang.org/pkg/time/#Minute
//
// 10. Converting a time value to a string returns the time formatted using the
// format string
//
//	"2006-01-02 15:04:05.999999999 -0700 MST"
//
// Order of evaluation
//
// When evaluating the operands of an expression or of function calls,
// operations are evaluated in lexical left-to-right order.
//
// For example, in the evaluation of
//
// 	g(h(), i()+x[j()], c)
//
// the function calls and evaluation of c happen in the order h(), i(), j(), c.
//
// Floating-point operations within a single expression are evaluated according
// to the associativity of the operators. Explicit parentheses affect the
// evaluation by overriding the default associativity. In the expression x + (y
// + z) the addition y + z is performed before adding x.
//
// Statements
//
// Statements control execution.
//
//  Statement =  EmptyStmt | AlterTableStmt | BeginTransactionStmt | CommitStmt
//  	| CreateIndexStmt | CreateTableStmt | DeleteFromStmt | DropIndexStmt
//  	| DropTableStmt | InsertIntoStmt | RollbackStmt | SelectStmt
//  	| TruncateTableStmt | UpdateStmt | ExplainStmt.
//
//  StatementList = Statement { ";" Statement } .
//
// Empty statements
//
// The empty statement does nothing.
//
//  EmptyStmt = .
//
// ALTER TABLE
//
// Alter table statements modify existing tables.  With the ADD clause it adds
// a new column to the table. The column must not exist. With the DROP clause
// it removes an existing column from a table. The column must exist and it
// must be not the only (last) column of the table. IOW, there cannot be a
// table with no columns.
//
//  AlterTableStmt = "ALTER" "TABLE" TableName ( "ADD" ColumnDef | "DROP" "COLUMN"  ColumnName ) .
//
// For example
//
//	BEGIN TRANSACTION;
// 		ALTER TABLE Stock ADD Qty int;
// 		ALTER TABLE Income DROP COLUMN Taxes;
//	COMMIT;
//
// When adding a column to a table with existing data, the constraint clause of
// the ColumnDef cannot be used. Adding a constrained column to an empty table
// is fine.
//
// BEGIN TRANSACTION
//
// Begin transactions statements introduce a new transaction level. Every
// transaction level must be eventually balanced by exactly one of COMMIT or
// ROLLBACK statements. Note that when a transaction is roll-backed because of
// a statement failure then no explicit balancing of the respective BEGIN
// TRANSACTION is statement is required nor permitted.
//
// Failure to properly balance any opened transaction level may cause dead
// locks and/or lose of data updated in the uppermost opened but never properly
// closed transaction level.
//
//  BeginTransactionStmt = "BEGIN" "TRANSACTION" .
//
// For example
//
//	BEGIN TRANSACTION;
//		INSERT INTO foo VALUES (42, 3.14);
//		INSERT INTO foo VALUES (-1, 2.78);
//	COMMIT;
//
// Mandatory transactions
//
// A database cannot be updated (mutated) outside of a transaction. Statements
// requiring a transaction
//
//	ALTER TABLE
//	COMMIT
//	CREATE INDEX
//	CREATE TABLE
//	DELETE FROM
//	DROP INDEX
//	DROP TABLE
//	INSERT INTO
//	ROLLBACK
//	TRUNCATE TABLE
//	UPDATE
//
// A database is effectively read only outside of a transaction. Statements not
// requiring a transaction
//
//	BEGIN TRANSACTION
//	SELECT FROM
//
// COMMIT
//
// The commit statement closes the innermost transaction nesting level. If
// that's the outermost level then the updates to the DB made by the
// transaction are atomically made persistent.
//
//  CommitStmt = "COMMIT" .
//
// For example
//
//	BEGIN TRANSACTION;
//		INSERT INTO AccountA (Amount) VALUES ($1);
//		INSERT INTO AccountB (Amount) VALUES (-$1);
//	COMMIT;
//
// CREATE INDEX
//
// Create index statements create new indices. Index is a named projection of
// ordered values of a table column to the respective records. As a special
// case the id() of the record can be indexed. Index name must not be the same
// as any of the existing tables and it also cannot be the same as of any
// column name of the table the index is on.
//
//  CreateIndexStmt = "CREATE" [ "UNIQUE" ] "INDEX" [ "IF" "NOT" "EXISTS" ]
//  	IndexName "ON" TableName "(" ExpressionList ")" .
//
// For example
//
//	BEGIN TRANSACTION;
//		CREATE TABLE Orders (CustomerID int, Date time);
//		CREATE INDEX OrdersID ON Orders (id());
//		CREATE INDEX OrdersDate ON Orders (Date);
//		CREATE TABLE Items (OrderID int, ProductID int, Qty int);
//		CREATE INDEX ItemsOrderID ON Items (OrderID);
//	COMMIT;
//
// Now certain SELECT statements may use the indices to speed up joins and/or
// to speed up record set filtering when the WHERE clause is used; or the
// indices might be used to improve the performance when the ORDER BY clause is
// present.
//
// The UNIQUE modifier requires the indexed values tuple to be index-wise
// unique or have all values NULL.
//
// The optional IF NOT EXISTS clause makes the statement a no operation if the
// index already exists.
//
// Simple index
//
// A simple index consists of only one expression which must be either a column
// name or the built-in id().
//
// Expression list index
//
// A more complex and more general index is one that consists of more than one
// expression or its single expression does not qualify as a simple index. In
// this case the type of all expressions in the list must be one of the non
// blob-like types.
//
// Note: Blob-like types are blob, bigint, bigrat, time and duration.
//
// CREATE TABLE
//
// Create table statements create new tables. A column definition declares the
// column name and type. Table names and column names are case sensitive.
// Neither a table or an index of the same name may exist in the DB.
//
//  CreateTableStmt = "CREATE" "TABLE" [ "IF" "NOT" "EXISTS" ] TableName
//  	"(" ColumnDef { "," ColumnDef } [ "," ] ")" .
//
//  ColumnDef = ColumnName Type [ "NOT" "NULL" | Expression ] [ "DEFAULT" Expression ] .
//  ColumnName = identifier .
//  TableName = identifier .
//
// For example
//
//	BEGIN TRANSACTION;
// 		CREATE TABLE department (
// 			DepartmentID   int,
// 			DepartmentName string,
// 		);
// 		CREATE TABLE employee (
// 			LastName	string,
// 			DepartmentID	int,
// 		);
//	COMMIT;
//
// The optional IF NOT EXISTS clause makes the statement a no operation if the
// table already exists.
//
// The optional constraint clause has two forms. The first one is found in many
// SQL dialects.
//
//	BEGIN TRANSACTION;
// 		CREATE TABLE department (
// 			DepartmentID   int,
// 			DepartmentName string NOT NULL,
// 		);
//	COMMIT;
//
// This form prevents the data in column DepartmentName to be NULL.
//
// The second form allows an arbitrary boolean expression to be used to
// validate the column. If the value of the expression is true then the
// validation succeeded. If the value of the expression is false or NULL then
// the validation fails. If the value of the expression is not of type bool an
// error occurs.
//
//	BEGIN TRANSACTION;
// 		CREATE TABLE department (
// 			DepartmentID   int,
// 			DepartmentName string DepartmentName IN ("HQ", "R/D", "Lab", "HR"),
// 		);
//	COMMIT;
//
//	BEGIN TRANSACTION;
// 		CREATE TABLE t (
//			TimeStamp time TimeStamp < now() && since(TimeStamp) < duration("10s"),
//			Event string Event != "" && Event like "[0-9]+:[ \t]+.*",
//		);
//	COMMIT;
//
// The optional DEFAULT clause is an expression which, if present, is
// substituted instead of a NULL value when the colum is assigned a value.
//
//	BEGIN TRANSACTION;
// 		CREATE TABLE department (
// 			DepartmentID   int,
// 			DepartmentName string DepartmentName IN ("HQ", "R/D", "Lab", "HR") DEFAULT "HQ",
// 		);
//	COMMIT;
//
// Note that the constraint and/or default expressions may refer to other
// columns by name:
//
//	BEGIN TRANSACTION;
//		CREATE TABLE t (
//			a int,
//			b int b > a && b < c DEFAULT (a+c)/2,
//			c int,
//	);
//	COMMIT;
//
//
// Constraints and defaults
//
// When a table row is inserted by the INSERT INTO statement or when a table
// row is updated by the UPDATE statement, the order of operations is as
// follows:
//
// 1. The new values of the affected columns are set and the values of all the
// row columns become the named values which can be referred to in default
// expressions evaluated in step 2.
//
// 2. If any row column value is NULL and the DEFAULT clause is present in the
// column's definition, the default expression is evaluated and its value is
// set as the respective column value.
//
// 3. The values, potentially updated, of row columns become the named values
// which can be referred to in constraint expressions evaluated during step 4.
//
// 4. All row columns which definition has the constraint clause present will
// have that constraint checked. If any constraint violation is detected, the
// overall operation fails and no changes to the table are made.
//
// DELETE FROM
//
// Delete from statements remove rows from a table, which must exist.
//
//  DeleteFromStmt = "DELETE" "FROM" TableName [ WhereClause ] .
//
// For example
//
//	BEGIN TRANSACTION;
//		DELETE FROM DepartmentID
//		WHERE DepartmentName == "Ponies";
//	COMMIT;
//
// If the WHERE clause is not present then all rows are removed and the
// statement is equivalent to the TRUNCATE TABLE statement.
//
// DROP INDEX
//
// Drop index statements remove indices from the DB. The index must exist.
//
//  DropIndexStmt = "DROP" "INDEX" [ "IF" "EXISTS" ] IndexName .
//  IndexName = identifier .
//
// For example
//
//	BEGIN TRANSACTION;
//		DROP INDEX ItemsOrderID;
//	COMMIT;
//
// The optional IF EXISTS clause makes the statement a no operation if the
// index does not exist.
//
// DROP TABLE
//
// Drop table statements remove tables from the DB. The table must exist.
//
//  DropTableStmt = "DROP" "TABLE" [ "IF" "EXISTS" ] TableName .
//
// For example
//
//	BEGIN TRANSACTION;
// 		DROP TABLE Inventory;
//	COMMIT;
//
// The optional IF EXISTS clause makes the statement a no operation if the
// table does not exist.
//
// INSERT INTO
//
// Insert into statements insert new rows into tables. New rows come from
// literal data, if using the VALUES clause, or are a result of select
// statement. In the later case the select statement is fully evaluated before
// the insertion of any rows is performed, allowing to insert values calculated
// from the same table rows are to be inserted into. If the ColumnNameList part
// is omitted then the number of values inserted in the row must be the same as
// are columns in the table. If the ColumnNameList part is present then the
// number of values per row must be same as the same number of column names.
// All other columns of the record are set to NULL.  The type of the value
// assigned to a column must be the same as is the column's type or the value
// must be NULL.
//
//  InsertIntoStmt = "INSERT" "INTO" TableName [ "(" ColumnNameList ")" ] ( Values | SelectStmt ) .
//
//  ColumnNameList = ColumnName { "," ColumnName } [ "," ] .
//  Values = "VALUES" "(" ExpressionList ")" { "," "(" ExpressionList ")" } [ "," ] .
//
// For example
//
//	BEGIN TRANSACTION;
// 		INSERT INTO department (DepartmentID) VALUES (42);
//
// 		INSERT INTO department (
// 			DepartmentName,
// 			DepartmentID,
// 		)
// 		VALUES (
// 			"R&D",
// 			42,
// 		);
//
// 		INSERT INTO department VALUES
//			(42, "R&D"),
//			(17, "Sales"),
// 		;
//	COMMIT;
//
//	BEGIN TRANSACTION;
//		INSERT INTO department (DepartmentName, DepartmentID)
//		SELECT DepartmentName+"/headquarters", DepartmentID+1000
//		FROM department;
//	COMMIT;
//
// If any of the columns of the table were defined using the optional
// constraints clause or the optional defaults clause then those are processed
// on a per row basis. The details are discussed in the "Constraints and
// defaults" chapter below the CREATE TABLE statement documentation.
//
// Explain statement
//
// Explain statement produces a recordset consisting of lines of text which
// describe the execution plan of a statement, if any.
//
//  ExplainStmt = "EXPLAIN" Statement .
//
// For example, the QL tool treats the explain statement specially and outputs
// the joined lines:
//
//	$ ql 'create table t(i int); create table u(j int)'
//	$ ql 'explain select * from t, u where t.i > 42 && u.j < 314'
//	┌Compute Cartesian product of
//	│   ┌Iterate all rows of table "t"
//	│   └Output field names ["i"]
//	│   ┌Iterate all rows of table "u"
//	│   └Output field names ["j"]
//	└Output field names ["t.i" "u.j"]
//	┌Filter on t.i > 42 && u.j < 314
//	│Possibly useful indices
//	│CREATE INDEX xt_i ON t(i);
//	│CREATE INDEX xu_j ON u(j);
//	└Output field names ["t.i" "u.j"]
//	$ ql 'CREATE INDEX xt_i ON t(i); CREATE INDEX xu_j ON u(j);'
//	$ ql 'explain select * from t, u where t.i > 42 && u.j < 314'
//	┌Compute Cartesian product of
//	│   ┌Iterate all rows of table "t" using index "xt_i" where i > 42
//	│   └Output field names ["i"]
//	│   ┌Iterate all rows of table "u" using index "xu_j" where j < 314
//	│   └Output field names ["j"]
//	└Output field names ["t.i" "u.j"]
//	$ ql 'explain select * from t where i > 12 and i between 10 and 20 and i < 42'
//	┌Iterate all rows of table "t" using index "xt_i" where i > 12 && i <= 20
//	└Output field names ["i"]
//	$
//
// The explanation may aid in uderstanding how a statement/query would be
// executed and if indices are used as expected - or which indices may possibly
// improve the statement performance.  The create index statements above were
// directly copy/pasted in the terminal from the suggestions provided by the
// filter recordset pipeline part returned by the explain statement.
//
// If the statement has nothing special in its plan, the result is the original
// statement.
//
//	$ ql 'explain delete from t where 42 < i'
//	DELETE FROM t WHERE i > 42;
//	$
//
// To get an explanation of the select statement of the IN predicate, use the EXPLAIN
// statement with that particular select statement.
//
//	$ ql 'explain select * from t where i in (select j from u where j > 0)'
//	┌Iterate all rows of table "t"
//	└Output field names ["i"]
//	┌Filter on i IN (SELECT j FROM u WHERE j > 0;)
//	└Output field names ["i"]
//	$ ql 'explain select j from u where j > 0'
//	┌Iterate all rows of table "u" using index "xu_j" where j > 0
//	└Output field names ["j"]
//	$
//
// ROLLBACK
//
// The rollback statement closes the innermost transaction nesting level
// discarding any updates to the DB made by it. If that's the outermost level
// then the effects on the DB are as if the transaction never happened.
//
//  RollbackStmt = "ROLLBACK" .
//
// For example
//
//	// First statement list
//	BEGIN TRANSACTION
//		SELECT * INTO tmp FROM foo;
//		INSERT INTO tmp SELECT * from bar;
//		SELECT * from tmp;
//
// The (temporary) record set from the last statement is returned and can be
// processed by the client.
//
//	// Second statement list
//	ROLLBACK;
//
// In this case the rollback is the same as 'DROP TABLE tmp;' but it can be a
// more complex operation.
//
// SELECT FROM
//
// Select from statements produce recordsets. The optional DISTINCT modifier
// ensures all rows in the result recordset are unique. Either all of the
// resulting fields are returned ('*') or only those named in FieldList.
//
// RecordSetList is a list of table names or parenthesized select statements,
// optionally (re)named using the AS clause.
//
// The result can be filtered using a WhereClause and orderd by the OrderBy
// clause.
//
//  SelectStmt = "SELECT" [ "DISTINCT" ] ( "*" | FieldList ) "FROM" RecordSetList
//  	[ JoinClause ] [ WhereClause ] [ GroupByClause ] [ OrderBy ] [ Limit ] [ Offset ].
//
//  JoinClause = ( "LEFT" | "RIGHT" | "FULL" ) [ "OUTER" ] "JOIN" RecordSet "ON" Expression .
//
//  RecordSet = ( TableName | "(" SelectStmt [ ";" ] ")" ) [ "AS" identifier ] .
//  RecordSetList = RecordSet { "," RecordSet } [ "," ] .
//
// For example
//
// 	SELECT * FROM Stock;
//
// 	SELECT DepartmentID
// 	FROM department
// 	WHERE DepartmentID == 42
// 	ORDER BY DepartmentName;
//
// 	SELECT employee.LastName
// 	FROM department, employee
// 	WHERE department.DepartmentID == employee.DepartmentID
// 	ORDER BY DepartmentID;
//
// If Recordset is a nested, parenthesized SelectStmt then it must be given a
// name using the AS clause if its field are to be accessible in expressions.
//
// 	SELECT a.b, c.d
// 	FROM
// 		x AS a,
// 		(
// 			SELECT * FROM y;
// 		) AS c
//	WHERE a.e > c.e;
//
// Fields naming rules
//
// A field is an named expression. Identifiers, not used as a type in
// conversion or a function name in the Call clause, denote names of (other)
// fields, values of which should be used in the expression.
//
//  Field = Expression [ "AS" identifier ] .
//
// The expression can be named using the AS clause.  If the AS clause is not
// present and the expression consists solely of a field name, then that field
// name is used as the name of the resulting field. Otherwise the field is
// unnamed.
//
// For example
//
//	SELECT 314, 42 as AUQLUE, DepartmentID, DepartmentID+1000, LastName as Name from employee;
//	// Fields are []string{"", "AUQLUE", "DepartmentID", "", "Name"}
//
// The SELECT statement can optionally enumerate the desired/resulting fields
// in a list.
//
//  FieldList = Field { "," Field } [ "," ] .
//
// No two identical field names can appear in the list.
//
//	SELECT DepartmentID, LastName, DepartmentID from employee;
//	// duplicate field name "DepartmentID"
//
//	SELECT DepartmentID, LastName, DepartmentID as ID2 from employee;
//	// works
//
// When more than one record set is used in the FROM clause record set list,
// the result record set field names are rewritten to be qualified using
// the record set names.
//
//	SELECT * FROM employee, department;
//	// Fields are []string{"employee.LastName", "employee.DepartmentID", "department.DepartmentID", "department.DepartmentName"
//
// If a particular record set doesn't have a name, its respective fields became
// unnamed.
//
//	SELECT * FROM employee as e, ( SELECT * FROM department);
//	// Fields are []string{"e.LastName", "e.DepartmentID", "", ""
//
//	SELECT * FROM employee AS e, ( SELECT * FROM department) AS d;
//	// Fields are []string{"e.LastName", "e.DepartmentID", "d.DepartmentID", "d.DepartmentName"
//
// Outer joins
//
// The optional JOIN clause, for example
//
//	SELECT *
//	FROM a
//	LEFT OUTER JOIN b ON expr;
//
// is mostly equal to
//
//	SELECT *
//	FROM a, b
//	WHERE expr;
//
// except that the rows from a which, when they appear in the cross join, never
// made expr to evaluate to true, are combined with a virtual row from b,
// containing all nulls, and added to the result set. For the RIGHT JOIN
// variant the discussed rules are used for rows from b not satisfying expr ==
// true and the virtual, all-null row "comes" from a. The FULL JOIN adds the
// respective rows which would be otherwise provided by the separate executions
// of the LEFT JOIN and RIGHT JOIN variants. For more thorough OUTER JOIN
// discussion please see the Wikipedia article at [10].
//
// Recordset ordering
//
// Resultins rows of a SELECT statement can be optionally ordered by the ORDER
// BY clause.  Collating proceeds by considering the expressions in the
// expression list left to right until a collating order is determined. Any
// possibly remaining expressions are not evaluated.
//
//  OrderBy = "ORDER" "BY" ExpressionList [ "ASC" | "DESC" ] .
//
// All of the expression values must yield an ordered type or NULL. Ordered
// types are defined in "Comparison operators". Collating of elements having a
// NULL value is different compared to what the comparison operators yield in
// expression evaluation (NULL result instead of a boolean value).
//
// Below, T denotes a non NULL value of any QL type.
//
// 	NULL < T
//
// NULL collates before any non NULL value (is considered smaller than T).
//
//	NULL == NULL
//
// Two NULLs have no collating order (are considered equal).
//
// Recordset filtering
//
// The WHERE clause restricts records considered by some statements, like
// SELECT FROM, DELETE FROM, or UPDATE.
//
//	expression value	consider the record
//	----------------	-------------------
//	true			yes
//	false or NULL		no
//
// It is an error if the expression evaluates to a non null value of non bool
// type.
//
//  WhereClause = "WHERE" Expression .
//
// Recordset grouping
//
// The GROUP BY clause is used to project rows having common values into a
// smaller set of rows.
//
// For example
//
//	SELECT Country, sum(Qty) FROM Sales GROUP BY Country;
//
//	SELECT Country, Product FROM Sales GROUP BY Country, Product;
//
//	SELECT DISTINCT Country, Product FROM Sales;
//
// Using the GROUP BY without any aggregate functions in the selected fields is
// in certain cases equal to using the DISTINCT modifier. The last two examples
// above produce the same resultsets.
//
//  GroupByClause = "GROUP BY" ColumnNameList .
//
// Skipping records
//
// The optional OFFSET clause allows to ignore first N records.  For example
//
//	SELECT * FROM t OFFSET 10;
//
// The above will produce only rows 11, 12, ... of the record set, if they
// exist. The value of the expression must a non negative integer, but not
// bigint or duration.
//
//  Offset = "OFFSET" Expression .
//
// Limiting the result set size
//
// The optional LIMIT clause allows to ignore all but first N records.  For
// example
//
//	SELECT * FROM t LIMIT 10;
//
// The above will return at most the first 10 records of the record set. The
// value of the expression must a non negative integer, but not bigint or
// duration.
//
//  Limit = "Limit" Expression .
//
// The LIMIT and OFFSET clauses can be combined. For example
//
//	SELECT * FROM t LIMIT 5 OFFSET 3;
//
// Considering table t has, say 10 records, the above will produce only records
// 4 - 8.
//
//	#1:	Ignore 1/3
//	#2:	Ignore 2/3
//	#3:	Ignore 3/3
//	#4:	Return 1/5
//	#5:	Return 2/5
//	#6:	Return 3/5
//	#7:	Return 4/5
//	#8:	Return 5/5
//
// After returning record #8, no more result rows/records are computed.
//
// Select statement evaluation order
//
// 1. The FROM clause is evaluated, producing a Cartesian product of its source
// record sets (tables or nested SELECT statements).
//
// 2. If present, the JOIN cluase is evaluated on the result set of the
// previous evaluation and the recordset specified by the JOIN clause. (...
// JOIN Recordset ON ...)
//
// 3. If present, the WHERE clause is evaluated on the result set of the
// previous evaluation.
//
// 4. If present, the GROUP BY clause is evaluated on the result set of the
// previous evaluation(s).
//
// 5. The SELECT field expressions are evaluated on the result set of the
// previous evaluation(s).
//
// 6. If present, the DISTINCT modifier is evaluated on the result set of the
// previous evaluation(s).
//
// 7. If present, the ORDER BY clause is evaluated on the result set of the
// previous evaluation(s).
//
// 8. If present, the OFFSET clause is evaluated on the result set of the
// previous evaluation(s). The offset expression is evaluated once for the
// first record produced by the previous evaluations.
//
// 9. If present, the LIMIT clause is evaluated on the result set of the
// previous evaluation(s). The limit expression is evaluated once for the first
// record produced by the previous evaluations.
//
//
// TRUNCATE TABLE
//
// Truncate table statements remove all records from a table. The table must
// exist.
//
//  TruncateTableStmt = "TRUNCATE" "TABLE" TableName .
//
// For example
//
//	BEGIN TRANSACTION
// 		TRUNCATE TABLE department;
//	COMMIT;
//
// UPDATE
//
// Update statements change values of fields in rows of a table.
//
//  UpdateStmt = "UPDATE" TableName [ "SET" ] AssignmentList [ WhereClause ] .
//
//  AssignmentList = Assignment { "," Assignment } [ "," ] .
//  Assignment = ColumnName "=" Expression .
//
// For example
//
//	BEGIN TRANSACTION
// 		UPDATE department
//			DepartmentName = DepartmentName + " dpt.",
//			DepartmentID = 1000+DepartmentID,
//		WHERE DepartmentID < 1000;
//	COMMIT;
//
// Note: The SET clause is optional.
//
// If any of the columns of the table were defined using the optional
// constraints clause or the optional defaults clause then those are processed
// on a per row basis. The details are discussed in the "Constraints and
// defaults" chapter below the CREATE TABLE statement documentation.
//
// System Tables
//
// To allow to query for DB meta data, there exist specially named tables, some
// of them being virtual.
//
// Note: Virtual system tables may have fake table-wise unique but meaningless
// and unstable record IDs. Do not apply the built-in id() to any system table.
//
// Tables Table
//
// The table __Table lists all tables in the DB. The schema is
//
//	CREATE TABLE __Table (Name string, Schema string);
//
// The Schema column returns the statement to (re)create table Name. This table
// is virtual.
//
// Columns Table
//
// The table __Colum lists all columns of all tables in the DB. The schema is
//
//	CREATE TABLE __Column (TableName string, Ordinal int, Name string, Type string);
//
// The Ordinal column defines the 1-based index of the column in the record.
// This table is virtual.
//
// Columns2 Table
//
// The table __Colum2 lists all columns of all tables in the DB which have the
// constraint NOT NULL or which have a constraint expression defined or which
// have a default expression defined. The schema is
//
//	CREATE TABLE __Column2 (TableName string, Name string, NotNull bool, ConstraintExpr string, DefaultExpr string)
//
// It's possible to obtain a consolidated recordset for all properties of all
// DB columns using
//
//	SELECT
//		__Column.TableName, __Column.Ordinal, __Column.Name, __Column.Type,
//		__Column2.NotNull, __Column2.ConstraintExpr, __Column2.DefaultExpr,
//	FROM __Column
//	LEFT JOIN __Column2
//	ON __Column.TableName == __Column2.TableName && __Column.Name == __Column2.Name
//	ORDER BY __Column.TableName, __Column.Ordinal;
//
// The Name column is the column name in TableName.
//
// Indices table
//
// The table __Index lists all indices in the DB. The schema is
//
//	CREATE TABLE __Index (TableName string, ColumnName string, Name string, IsUnique bool);
//
// The IsUnique columns reflects if the index was created using the optional
// UNIQUE clause. This table is virtual.
//
// Built-in functions
//
// Built-in functions are predeclared.
//
// Average
//
// The built-in aggregate function avg returns the average of values of an
// expression.  Avg ignores NULL values, but returns NULL if all values of a
// column are NULL or if avg is applied to an empty record set.
//
// 	func avg(e numeric) typeof(e)
//
// The column values must be of a numeric type.
//
//	SELECT salesperson, avg(sales) FROM salesforce GROUP BY salesperson;
//
// Contains
//
// The built-in function contains returns true if substr is within s.
//
//	func contains(s, substr string) bool
//
// If any argument to contains is NULL the result is NULL.
//
// Count
//
// The built-in aggregate function count returns how many times an expression
// has a non NULL values or the number of rows in a record set. Note: count()
// returns 0 for an empty record set.
//
//	func count() int             // The number of rows in a record set.
//	func count(*) int            // Equivalent to count().
// 	func count(e expression) int // The number of cases where the expression value is not NULL.
//
// For example
//
//	SELECT count() FROM department; // # of rows
//
//	SELECT count(*) FROM department; // # of rows
//
//	SELECT count(DepartmentID) FROM department; // # of records with non NULL field DepartmentID
//
//	SELECT count()-count(DepartmentID) FROM department; // # of records with NULL field DepartmentID
//
//	SELECT count(foo+bar*3) AS y FROM t; // # of cases where 'foo+bar*3' is non NULL
//
// Date
//
// Date returns the time corresponding to
//
//	yyyy-mm-dd hh:mm:ss + nsec nanoseconds
//
// in the appropriate zone for that time in the given location.
//
// The month, day, hour, min, sec, and nsec values may be outside their usual
// ranges and will be normalized during the conversion. For example, October 32
// converts to November 1.
//
// A daylight savings time transition skips or repeats times. For example, in
// the United States, March 13, 2011 2:15am never occurred, while November 6,
// 2011 1:15am occurred twice. In such cases, the choice of time zone, and
// therefore the time, is not well-defined. Date returns a time that is correct
// in one of the two zones involved in the transition, but it does not
// guarantee which.
//
// 	func date(year, month, day, hour, min, sec, nsec int, loc string) time
//
// A location maps time instants to the zone in use at that time. Typically,
// the location represents the collection of time offsets in use in a
// geographical area, such as "CEST" and "CET" for central Europe.  "local"
// represents the system's local time zone. "UTC" represents Universal
// Coordinated Time (UTC).
//
// The month specifies a month of the year (January = 1, ...).
//
// If any argument to date is NULL the result is NULL.
//
// Day
//
// The built-in function day returns the day of the month specified by t.
//
// 	func day(t time) int
//
// If the argument to day is NULL the result is NULL.
//
// Format time
//
// The built-in function formatTime returns a textual representation of the
// time value formatted according to layout, which defines the format by
// showing how the reference time,
//
//	Mon Jan 2 15:04:05 -0700 MST 2006
//
// would be displayed if it were the value; it serves as an example of the
// desired output. The same display rules will then be applied to the time
// value.
//
// 	func formatTime(t time, layout string) string
//
// If any argument to formatTime is NULL the result is NULL.
//
// NOTE: The string value of the time zone, like "CET" or "ACDT", is dependent
// on the time zone of the machine the function is run on. For example, if the
// t value is in "CET", but the machine is in "ACDT", instead of "CET" the
// result is "+0100". This is the same what Go (time.Time).String() returns and
// in fact formatTime directly calls t.String().
//
//	formatTime(date(2006, 1, 2, 15, 4, 5, 999999999, "CET"))
//
// returns
//
//	2006-01-02 15:04:05.999999999 +0100 CET
//
// on a machine in the CET time zone, but may return
//
//	2006-01-02 15:04:05.999999999 +0100 +0100
//
// on a machine in the ACDT zone. The time value is in both cases the same so
// its ordering and comparing is correct. Only the display value can differ.
//
// Format numbers
//
// The built-in functions formatFloat and formatInt format numbers
// to strings using go's number format functions in the `strconv` package. For
// all three functions, only the first argument is mandatory. The default values
// of the rest are shown in the examples. If the first argument is NULL, the
// result is NULL.
//
//	formatFloat(43.2[, 'g', -1, 64]) string
//
// returns
//
//	"43.2"
//
//	formatInt(-42[, 10]) string
//
// returns
//
//	"-42"
//
//	formatInt(uint32(42)[, 10]) string
//
// returns
//
//	"42"
//
// Unlike the `strconv` equivalent, the formatInt function handles all integer
// types, both signed and unsigned.
//
// HasPrefix
//
// The built-in function hasPrefix tests whether the string s begins with prefix.
//
//	func hasPrefix(s, prefix string) bool
//
// If any argument to hasPrefix is NULL the result is NULL.
//
// HasSuffix
//
// The built-in function hasSuffix tests whether the string s ends with suffix.
//
//	func hasSuffix(s, suffix string) bool
//
// If any argument to hasSuffix is NULL the result is NULL.
//
// Hour
//
// The built-in function hour returns the hour within the day specified by t,
// in the range [0, 23].
//
// 	func hour(t time) int
//
// If the argument to hour is NULL the result is NULL.
//
// Hours
//
// The built-in function hours returns the duration as a floating point number
// of hours.
//
// 	func hours(d duration) float
//
// If the argument to hours is NULL the result is NULL.
//
// Record id
//
// The built-in function id takes zero or one arguments. If no argument is
// provided, id() returns a table-unique automatically assigned numeric
// identifier of type int. Ids of deleted records are not reused unless the DB
// becomes completely empty (has no tables).
//
// 	func id() int
//
// For example
//
// 	SELECT id(), LastName
// 	FROM employee;
//
// If id() without arguments is called for a row which is not a table record
// then the result value is NULL.
//
// For example
//
//	SELECT id(), e.LastName, e.DepartmentID, d.DepartmentID
//	FROM
//		employee AS e,
//		department AS d,
//	WHERE e.DepartmentID == d.DepartmentID;
//	// Will always return NULL in first field.
//
//	SELECT e.ID, e.LastName, e.DepartmentID, d.DepartmentID
//	FROM
//		(SELECT id() AS ID, LastName, DepartmentID FROM employee) AS e,
//		department as d,
//	WHERE e.DepartmentID == d.DepartmentID;
//	// Will work.
//
// If id() has one argument it must be a table name of a table in a cross join.
//
// For example
//
// 	SELECT *
// 	FROM foo, bar
// 	WHERE bar.fooID == id(foo)
// 	ORDER BY id(foo);
//
// Length
//
// The built-in function len takes a string argument and returns the lentgh of
// the string in bytes.
//
// 	func len(s string) int
//
// The expression len(s) is constant if s is a string constant.
//
// If the argument to len is NULL the result is NULL.
//
// Maximum
//
// The built-in aggregate function max returns the largest value of an
// expression in a record set.  Max ignores NULL values, but returns NULL if
// all values of a column are NULL or if max is applied to an empty record set.
//
// 	func max(e expression) typeof(e) // The largest value of the expression.
//
// The expression values must be of an ordered type.
//
// For example
//
//	SELECT department, max(sales) FROM t GROUP BY department;
//
// Minimum
//
// The built-in aggregate function min returns the smallest value of an
// expression in a record set.  Min ignores NULL values, but returns NULL if
// all values of a column are NULL or if min is applied to an empty record set.
//
// 	func min(e expression) typeof(e) // The smallest value of the expression.
//
// For example
//
//	SELECT a, min(b) FROM t GROUP BY a;
//
// The column values must be of an ordered type.
//
// Minute
//
// The built-in function minute returns the minute offset within the hour
// specified by t, in the range [0, 59].
//
// 	func minute(t time) int
//
// If the argument to minute is NULL the result is NULL.
//
// Minutes
//
// The built-in function minutes returns the duration as a floating point
// number of minutes.
//
// 	func minutes(d duration) float
//
// If the argument to minutes is NULL the result is NULL.
//
// Month
//
// The built-in function month returns the month of the year specified by t
// (January = 1, ...).
//
// 	func month(t time) int
//
// If the argument to month is NULL the result is NULL.
//
// Nanosecond
//
// The built-in function nanosecond returns the nanosecond offset within the
// second specified by t, in the range [0, 999999999].
//
// 	func nanosecond(t time) int
//
// If the argument to nanosecond is NULL the result is NULL.
//
// Nanoseconds
//
// The built-in function nanoseconds returns the duration as an integer
// nanosecond count.
//
// 	func nanoseconds(d duration) float
//
// If the argument to nanoseconds is NULL the result is NULL.
//
// Now
//
// The built-in function now returns the current local time.
//
// 	func now() time
//
// Parse time
//
// The built-in function parseTime parses a formatted string and returns the
// time value it represents. The layout defines the format by showing how the
// reference time,
//
//	Mon Jan 2 15:04:05 -0700 MST 2006
//
// would be interpreted if it were the value; it serves as an example of the
// input format. The same interpretation will then be made to the input string.
//
// Elements omitted from the value are assumed to be zero or, when zero is
// impossible, one, so parsing "3:04pm" returns the time corresponding to Jan
// 1, year 0, 15:04:00 UTC (note that because the year is 0, this time is
// before the zero Time). Years must be in the range 0000..9999. The day of the
// week is checked for syntax but it is otherwise ignored.
//
// In the absence of a time zone indicator, parseTime returns a time in UTC.
//
// When parsing a time with a zone offset like -0700, if the offset corresponds
// to a time zone used by the current location, then parseTime uses that
// location and zone in the returned time. Otherwise it records the time as
// being in a fabricated location with time fixed at the given zone offset.
//
// When parsing a time with a zone abbreviation like MST, if the zone
// abbreviation has a defined offset in the current location, then that offset
// is used. The zone abbreviation "UTC" is recognized as UTC regardless of
// location. If the zone abbreviation is unknown, Parse records the time as
// being in a fabricated location with the given zone abbreviation and a zero
// offset. This choice means that such a time can be parses and reformatted
// with the same layout losslessly, but the exact instant used in the
// representation will differ by the actual zone offset. To avoid such
// problems, prefer time layouts that use a numeric zone offset.
//
// 	func parseTime(layout, value string) time
//
// If any argument to parseTime is NULL the result is NULL.
//
// Second
//
// The built-in function second returns the second offset within the minute
// specified by t, in the range [0, 59].
//
// 	func second(t time) int
//
// If the argument to second is NULL the result is NULL.
//
// Seconds
//
// The built-in function seconds returns the duration as a floating point
// number of seconds.
//
// 	func seconds(d duration) float
//
// If the argument to seconds is NULL the result is NULL.
//
// Since
//
// The built-in function since returns the time elapsed since t. It is
// shorthand for now()-t.
//
// 	func since(t time) duration
//
// If the argument to since is NULL the result is NULL.
//
// Sum
//
// The built-in aggregate function sum returns the sum of values of an
// expression for all rows of a record set. Sum ignores NULL values, but
// returns NULL if all values of a column are NULL or if sum is applied to an
// empty record set.
//
// 	func sum(e expression) typeof(e) // The sum of the values of the expression.
//
// The column values must be of a numeric type.
//
//	SELECT salesperson, sum(sales) FROM salesforce GROUP BY salesperson;
//
// Time in a specific zone
//
// The built-in function timeIn returns t with the location information set to
// loc. For discussion of the loc argument please see date().
//
// 	func timeIn(t time, loc string) time
//
// If any argument to timeIn is NULL the result is NULL.
//
// Weekday
//
// The built-in function weekday returns the day of the week specified by t.
// Sunday == 0, Monday == 1, ...
//
// 	func weekday(t time) int
//
// If the argument to weekday is NULL the result is NULL.
//
// Year
//
// The built-in function year returns the year in which t occurs.
//
// 	func year(t time) int
//
// If the argument to year is NULL the result is NULL.
//
// Year day
//
// The built-in function yearDay returns the day of the year specified by t, in
// the range [1,365] for non-leap years, and [1,366] in leap years.
//
// 	func yearDay(t time) int
//
// If the argument to yearDay is NULL the result is NULL.
//
// Manipulating complex numbers
//
// Three functions assemble and disassemble complex numbers. The built-in
// function complex constructs a complex value from a floating-point real and
// imaginary part, while real and imag extract the real and imaginary parts of
// a complex value.
//
// 	complex(realPart, imaginaryPart floatT) complexT
// 	real(complexT) floatT
// 	imag(complexT) floatT
//
// The type of the arguments and return value correspond. For complex, the two
// arguments must be of the same floating-point type and the return type is the
// complex type with the corresponding floating-point constituents: complex64
// for float32, complex128 for float64. The real and imag functions together
// form the inverse, so for a complex value z, z == complex(real(z), imag(z)).
//
// If the operands of these functions are all constants, the return value is a
// constant.
//
// 	complex(2, -2)             	// complex128
// 	complex(1.0, -1.4)         	// complex128
// 	float32(math.Cos(math.Pi/2))  	// float32
// 	complex(5, float32(-x))         // complex64
// 	imag(b)                   	// float64
// 	real(complex(5, float32(-x)))   // float32
//
// If any argument to any of complex, real, imag functions is NULL the result
// is NULL.
//
// Size guarantees
//
// For the numeric types, the following sizes are guaranteed
//
// 	type                                            size in bytes
//
// 	byte, uint8, int8                                1
// 	uint16, int16                                    2
// 	uint32, int32, float32                           4
// 	uint, uint64, int, int64, float64, complex64     8
// 	complex128                                      16
//
// License
//
// Portions of this specification page are modifications based on work[2]
// created and shared by Google[3] and used according to terms described in the
// Creative Commons 3.0 Attribution License[4].
//
// This specification is licensed under the Creative Commons Attribution 3.0
// License, and code is licensed under a BSD license[5].
//
// References
//
// Links from the above documentation
//
// 	[1]: http://golang.org/ref/spec#Notation
//	[2]: http://golang.org/ref/spec
//	[3]: http://code.google.com/policies.html
//	[4]: http://creativecommons.org/licenses/by/3.0/
//	[5]: http://golang.org/LICENSE
//	[6]: http://golang.org/pkg/regexp/#Regexp.MatchString
//	[7]: http://developer.mimer.com/validator/sql-reserved-words.tml
//	[8]: http://godoc.org/github.com/cznic/zappy
//	[9]: http://www.w3schools.com/sql/sql_default.asp
//	[10]: http://en.wikipedia.org/wiki/Join_(SQL)#Outer_join
//
// Implementation details
//
// This section is not part of the specification.
//
// Indices
//
// WARNING: The implementation of indices is new and it surely needs more time
// to become mature.
//
// Indices are used currently used only by the WHERE clause. The following
// expression patterns of 'WHERE expression' are recognized and trigger index
// use.
//
// 	- WHERE c                   // For bool typed indexed column c
// 	- WHERE !c                  // For bool typed indexed column c
// 	- WHERE c relOp constExpr   // For indexed column c
// 	- WHERE c relOp parameter   // For indexed column c
// 	- WHERE parameter relOp c   // For indexed column c
// 	- WHERE constExpr relOp c   // For indexed column c
//
// The relOp is one of the relation operators <, <=, ==, >=, >. For the
// equality operator both operands must be of comparable types. For all other
// operators both operands must be of ordered types. The constant expression is
// a compile time constant expression. Some constant folding is still a TODO.
// Parameter is a QL parameter ($1 etc.).
//
// Query rewriting
//
// Consider tables t and u, both with an indexed field f. The WHERE expression
// doesn't comply with the above simple detected cases.
//
//	SELECT * FROM t, u WHERE t.f < x && u.f < y;
//
// However, such query is now automatically rewritten to
//
//	SELECT * FROM
//		(SELECT * FROM t WHERE f < x),
//		(SELECT * FROM u WHERE f < y);
//
// which will use both of the indices. The impact of using the indices can be
// substantial (cf.  BenchmarkCrossJoin*) if the resulting rows have low
// "selectivity", ie. only few rows from both tables are selected by the
// respective WHERE filtering.
//
// Note: Existing QL DBs can be used and indices can be added to them. However,
// once any indices are present in the DB, the old QL versions cannot work with
// such DB anymore.
//
// Benchmarks
//
// Running a benchmark with -v (-test.v) outputs information about the scale
// used to report records/s and a brief description of the benchmark. For
// example
//
//	$ go test -run NONE -bench 'SelectMem.*1e[23]' -v
//	PASS
//	BenchmarkSelectMem1kBx1e2	   50000	     67680 ns/op	1477537.05 MB/s
//	--- BENCH: BenchmarkSelectMem1kBx1e2
//		all_test.go:310:
//			=============================================================
//			NOTE: All benchmarks report records/s as 1000000 bytes/s.
//			=============================================================
//		all_test.go:321: Having a table of 100 records, each of size 1kB, measure the performance of
//			SELECT * FROM t;
//
//	BenchmarkSelectMem1kBx1e3	    5000	    634819 ns/op	1575251.01 MB/s
//	--- BENCH: BenchmarkSelectMem1kBx1e3
//		all_test.go:321: Having a table of 1000 records, each of size 1kB, measure the performance of
//			SELECT * FROM t;
//
//	ok  	github.com/cznic/ql	7.496s
//	$
//
// Running the full suite of benchmarks takes a lot of time. Use the -timeout
// flag to avoid them being killed after the default time limit (10 minutes).
package ql