inspect: remove redundant join conditions

The TABLE_SCHEMA and TABLE_NAME are already guaranteed to have the same value in COLUMNS and UNIQUES because of the WHEREs in each query. Dropping it from the ON clause makes it complete much faster.

On (at least) MySQL 5.6 installs with thousands of tables, this query completes in a few seconds without the additional join conditions, but takes more than a minute with it.

go/logic/inspect.go

@@ -622,8 +622,6 @@ func (this *Inspector) getCandidateUniqueKeys(tableName string) (uniqueKeys [](*
       GROUP BY TABLE_SCHEMA, TABLE_NAME, INDEX_NAME
     ) AS UNIQUES
     ON (
-      COLUMNS.TABLE_SCHEMA = UNIQUES.TABLE_SCHEMA AND
-      COLUMNS.TABLE_NAME = UNIQUES.TABLE_NAME AND
       COLUMNS.COLUMN_NAME = UNIQUES.FIRST_COLUMN_NAME
     )
     WHERE