diff --git a/go/logic/applier.go b/go/logic/applier.go
index aee2129..89e1995 100644
--- a/go/logic/applier.go
+++ b/go/logic/applier.go
@@ -8,6 +8,7 @@ package logic
 import (
 	gosql "database/sql"
 	"fmt"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -122,17 +123,16 @@ func (this *Applier) validateAndReadTimeZone() error {
 // - User may skip strict mode
 // - User may allow zero dats or zero in dates
 func (this *Applier) generateSqlModeQuery() string {
-	sqlModeAddendum := `,NO_AUTO_VALUE_ON_ZERO`
+	sqlModeAddendum := []string{`NO_AUTO_VALUE_ON_ZERO`}
 	if !this.migrationContext.SkipStrictMode {
-		sqlModeAddendum = fmt.Sprintf("%s,STRICT_ALL_TABLES", sqlModeAddendum)
+		sqlModeAddendum = append(sqlModeAddendum, `STRICT_ALL_TABLES`)
 	}
-	sqlModeQuery := fmt.Sprintf("CONCAT(@@session.sql_mode, ',%s')", sqlModeAddendum)
+	sqlModeQuery := fmt.Sprintf("CONCAT(@@session.sql_mode, ',%s')", strings.Join(sqlModeAddendum, ","))
 	if this.migrationContext.AllowZeroInDate {
 		sqlModeQuery = fmt.Sprintf("REPLACE(REPLACE(%s, 'NO_ZERO_IN_DATE', ''), 'NO_ZERO_DATE', '')", sqlModeQuery)
 	}
-	sqlModeQuery = fmt.Sprintf("sql_mode = %s", sqlModeQuery)
 
-	return sqlModeQuery
+	return fmt.Sprintf("sql_mode = %s", sqlModeQuery)
 }
 
 // readTableColumns reads table columns on applier
diff --git a/go/logic/applier_test.go b/go/logic/applier_test.go
new file mode 100644
index 0000000..a2c1414
--- /dev/null
+++ b/go/logic/applier_test.go
@@ -0,0 +1,172 @@
+/*
+   Copyright 2022 GitHub Inc.
+         See https://github.com/github/gh-ost/blob/master/LICENSE
+*/
+
+package logic
+
+import (
+	"strings"
+	"testing"
+
+	test "github.com/openark/golib/tests"
+
+	"github.com/github/gh-ost/go/base"
+	"github.com/github/gh-ost/go/binlog"
+	"github.com/github/gh-ost/go/sql"
+)
+
+func TestApplierGenerateSqlModeQuery(t *testing.T) {
+	migrationContext := base.NewMigrationContext()
+	applier := NewApplier(migrationContext)
+
+	{
+		test.S(t).ExpectEquals(
+			applier.generateSqlModeQuery(),
+			`sql_mode = CONCAT(@@session.sql_mode, ',NO_AUTO_VALUE_ON_ZERO,STRICT_ALL_TABLES')`,
+		)
+	}
+	{
+		migrationContext.SkipStrictMode = true
+		migrationContext.AllowZeroInDate = false
+		test.S(t).ExpectEquals(
+			applier.generateSqlModeQuery(),
+			`sql_mode = CONCAT(@@session.sql_mode, ',NO_AUTO_VALUE_ON_ZERO')`,
+		)
+	}
+	{
+		migrationContext.SkipStrictMode = false
+		migrationContext.AllowZeroInDate = true
+		test.S(t).ExpectEquals(
+			applier.generateSqlModeQuery(),
+			`sql_mode = REPLACE(REPLACE(CONCAT(@@session.sql_mode, ',NO_AUTO_VALUE_ON_ZERO,STRICT_ALL_TABLES'), 'NO_ZERO_IN_DATE', ''), 'NO_ZERO_DATE', '')`,
+		)
+	}
+	{
+		migrationContext.SkipStrictMode = true
+		migrationContext.AllowZeroInDate = true
+		test.S(t).ExpectEquals(
+			applier.generateSqlModeQuery(),
+			`sql_mode = REPLACE(REPLACE(CONCAT(@@session.sql_mode, ',NO_AUTO_VALUE_ON_ZERO'), 'NO_ZERO_IN_DATE', ''), 'NO_ZERO_DATE', '')`,
+		)
+	}
+}
+
+func TestApplierUpdateModifiesUniqueKeyColumns(t *testing.T) {
+	columns := sql.NewColumnList([]string{"id", "item_id"})
+	columnValues := sql.ToColumnValues([]interface{}{123456, 42})
+
+	migrationContext := base.NewMigrationContext()
+	migrationContext.OriginalTableColumns = columns
+	migrationContext.UniqueKey = &sql.UniqueKey{
+		Name:    t.Name(),
+		Columns: *columns,
+	}
+
+	applier := NewApplier(migrationContext)
+
+	t.Run("unmodified", func(t *testing.T) {
+		modifiedColumn, isModified := applier.updateModifiesUniqueKeyColumns(&binlog.BinlogDMLEvent{
+			DatabaseName:      "test",
+			DML:               binlog.UpdateDML,
+			NewColumnValues:   columnValues,
+			WhereColumnValues: columnValues,
+		})
+		test.S(t).ExpectEquals(modifiedColumn, "")
+		test.S(t).ExpectFalse(isModified)
+	})
+
+	t.Run("modified", func(t *testing.T) {
+		modifiedColumn, isModified := applier.updateModifiesUniqueKeyColumns(&binlog.BinlogDMLEvent{
+			DatabaseName:      "test",
+			DML:               binlog.UpdateDML,
+			NewColumnValues:   sql.ToColumnValues([]interface{}{123456, 24}),
+			WhereColumnValues: columnValues,
+		})
+		test.S(t).ExpectEquals(modifiedColumn, "item_id")
+		test.S(t).ExpectTrue(isModified)
+	})
+}
+
+func TestApplierBuildDMLEventQuery(t *testing.T) {
+	columns := sql.NewColumnList([]string{"id", "item_id"})
+	columnValues := sql.ToColumnValues([]interface{}{123456, 42})
+
+	migrationContext := base.NewMigrationContext()
+	migrationContext.OriginalTableName = "test"
+	migrationContext.OriginalTableColumns = columns
+	migrationContext.SharedColumns = columns
+	migrationContext.MappedSharedColumns = columns
+	migrationContext.UniqueKey = &sql.UniqueKey{
+		Name:    t.Name(),
+		Columns: *columns,
+	}
+
+	applier := NewApplier(migrationContext)
+
+	t.Run("delete", func(t *testing.T) {
+		binlogEvent := &binlog.BinlogDMLEvent{
+			DatabaseName:      "test",
+			DML:               binlog.DeleteDML,
+			WhereColumnValues: columnValues,
+		}
+
+		res := applier.buildDMLEventQuery(binlogEvent)
+		test.S(t).ExpectEquals(len(res), 1)
+		test.S(t).ExpectNil(res[0].err)
+		test.S(t).ExpectEquals(strings.TrimSpace(res[0].query),
+			`delete /* gh-ost `+"`test`.`_test_gho`"+` */
+				from
+					`+"`test`.`_test_gho`"+`
+				where
+					((`+"`id`"+` = ?) and (`+"`item_id`"+` = ?))`)
+
+		test.S(t).ExpectEquals(len(res[0].args), 2)
+		test.S(t).ExpectEquals(res[0].args[0], 123456)
+		test.S(t).ExpectEquals(res[0].args[1], 42)
+	})
+
+	t.Run("insert", func(t *testing.T) {
+		binlogEvent := &binlog.BinlogDMLEvent{
+			DatabaseName:    "test",
+			DML:             binlog.InsertDML,
+			NewColumnValues: columnValues,
+		}
+		res := applier.buildDMLEventQuery(binlogEvent)
+		test.S(t).ExpectEquals(len(res), 1)
+		test.S(t).ExpectNil(res[0].err)
+		test.S(t).ExpectEquals(strings.TrimSpace(res[0].query),
+			`replace /* gh-ost `+"`test`.`_test_gho`"+` */ into
+				`+"`test`.`_test_gho`"+`
+					`+"(`id`, `item_id`)"+`
+				values
+					(?, ?)`)
+		test.S(t).ExpectEquals(len(res[0].args), 2)
+		test.S(t).ExpectEquals(res[0].args[0], 123456)
+		test.S(t).ExpectEquals(res[0].args[1], 42)
+	})
+
+	t.Run("update", func(t *testing.T) {
+		binlogEvent := &binlog.BinlogDMLEvent{
+			DatabaseName:      "test",
+			DML:               binlog.UpdateDML,
+			NewColumnValues:   columnValues,
+			WhereColumnValues: columnValues,
+		}
+		res := applier.buildDMLEventQuery(binlogEvent)
+		test.S(t).ExpectEquals(len(res), 1)
+		test.S(t).ExpectNil(res[0].err)
+		test.S(t).ExpectEquals(strings.TrimSpace(res[0].query),
+			`update /* gh-ost `+"`test`.`_test_gho`"+` */
+					`+"`test`.`_test_gho`"+`
+				set
+					`+"`id`"+`=?, `+"`item_id`"+`=?
+				where
+					((`+"`id`"+` = ?) and (`+"`item_id`"+` = ?))`)
+		test.S(t).ExpectEquals(len(res[0].args), 4)
+		test.S(t).ExpectEquals(res[0].args[0], 123456)
+		test.S(t).ExpectEquals(res[0].args[1], 42)
+		test.S(t).ExpectEquals(res[0].args[2], 123456)
+		test.S(t).ExpectEquals(res[0].args[3], 42)
+	})
+}
diff --git a/go/sql/builder.go b/go/sql/builder.go
index 025d4a8..0169390 100644
--- a/go/sql/builder.go
+++ b/go/sql/builder.go
@@ -505,13 +505,13 @@ func BuildDMLUpdateQuery(databaseName, tableName string, tableColumns, sharedCol
 		return "", sharedArgs, uniqueKeyArgs, err
 	}
 	result = fmt.Sprintf(`
- 			update /* gh-ost %s.%s */
- 					%s.%s
+			update /* gh-ost %s.%s */
+					%s.%s
 				set
 					%s
 				where
- 					%s
- 		`, databaseName, tableName,
+					%s
+		`, databaseName, tableName,
 		databaseName, tableName,
 		setClause,
 		equalsComparison,