Index: src/select.c ================================================================== --- src/select.c +++ src/select.c @@ -3294,72 +3294,75 @@ ** The code generated for this simplification gives the same result ** but only has to scan the data once. And because indices might ** exist on the table t1, a complete scan of the data might be ** avoided. ** -** Flattening is only attempted if all of the following are true: +** Flattening is subject to the following constraints: ** -** (1) The subquery and the outer query do not both use aggregates. +** (1) The subquery and the outer query cannot both be aggregates. ** -** (2) The subquery is not an aggregate or (2a) the outer query is not a join -** and (2b) the outer query does not use subqueries other than the one -** FROM-clause subquery that is a candidate for flattening. (2b is -** due to ticket [2f7170d73bf9abf80] from 2015-02-09.) +** (2) If the subquery is an aggregate then +** (2a) the outer query must not be a join and +** (2b) the outer query must not use subqueries +** other than the one FROM-clause subquery that is a candidate +** for flattening. (This is due to ticket [2f7170d73bf9abf80] +** from 2015-02-09.) ** -** (3) The subquery is not the right operand of a LEFT JOIN -** or (a) the subquery is not itself a join and (b) the FROM clause -** of the subquery does not contain a virtual table and (c) the -** outer query is not an aggregate. +** (3) If the subquery is the right operand of a LEFT JOIN then +** (3a) the subquery may not be a join and +** (3b) the FROM clause of the subquery may not contain a virtual +** table and +** (3c) the outer query may not be an aggregate. ** -** (4) The subquery is not DISTINCT. +** (4) The subquery can not be DISTINCT. ** ** (**) At one point restrictions (4) and (5) defined a subset of DISTINCT ** sub-queries that were excluded from this optimization. Restriction ** (4) has since been expanded to exclude all DISTINCT subqueries. ** -** (6) The subquery does not use aggregates or the outer query is not -** DISTINCT. +** (6) If the subquery is aggregate, the outer query may not be DISTINCT. ** -** (7) The subquery has a FROM clause. TODO: For subqueries without +** (7) The subquery must have a FROM clause. TODO: For subqueries without ** A FROM clause, consider adding a FROM clause with the special ** table sqlite_once that consists of a single row containing a ** single NULL. ** -** (8) The subquery does not use LIMIT or the outer query is not a join. +** (8) If the subquery uses LIMIT then the outer query may not be a join. ** -** (9) The subquery does not use LIMIT or the outer query does not use -** aggregates. +** (9) If the subquery uses LIMIT then the outer query may not be aggregate. ** ** (**) Restriction (10) was removed from the code on 2005-02-05 but we ** accidently carried the comment forward until 2014-09-15. Original -** text: "The subquery does not use aggregates or the outer query -** does not use LIMIT." +** constraint: "If the subquery is aggregate then the outer query +** may not use LIMIT." ** -** (11) The subquery and the outer query do not both have ORDER BY clauses. +** (11) The subquery and the outer query may not both have ORDER BY clauses. ** ** (**) Not implemented. Subsumed into restriction (3). Was previously ** a separate restriction deriving from ticket #350. ** -** (13) The subquery and outer query do not both use LIMIT. +** (13) The subquery and outer query may not both use LIMIT. ** -** (14) The subquery does not use OFFSET. +** (14) The subquery may not use OFFSET. ** -** (15) The outer query is not part of a compound select or the -** subquery does not have a LIMIT clause. +** (15) If the outer query is part of a compound select, then the +** subquery may not use LIMIT. ** (See ticket #2339 and ticket [02a8e81d44]). ** -** (16) The outer query is not an aggregate or the subquery does -** not contain ORDER BY. (Ticket #2942) This used to not matter +** (16) If the outer query is aggregate, then the subquery may not +** use ORDER BY. (Ticket #2942) This used to not matter ** until we introduced the group_concat() function. ** -** (17) The sub-query is not a compound select, or it is a UNION ALL -** compound clause made up entirely of non-aggregate queries, and -** the parent query: -** -** * is not itself part of a compound select, -** * is not an aggregate or DISTINCT query, and -** * is not a join +** (17) If the subquery is a compound select, then +** (17a) all compound operators must be a UNION ALL, and +** (17b) no terms within the subquery compound may be aggregate +** or DISTINT, and +** (17c) every term within the subquery compound must have a FROM clause +** (17d) the outer query may not be +** (17d1) aggregate, or +** (17d2) DISTINCT, or +** (17d3) a join. ** ** The parent and sub-query may contain WHERE clauses. Subject to ** rules (11), (13) and (14), they may also contain ORDER BY, ** LIMIT and OFFSET clauses. The subquery cannot use any compound ** operator other than UNION ALL because all the other compound @@ -3371,33 +3374,33 @@ ** SELECT statement, but all the code here does is make sure that no ** such (illegal) sub-query is flattened. The caller will detect the ** syntax error and return a detailed message. ** ** (18) If the sub-query is a compound select, then all terms of the -** ORDER by clause of the parent must be simple references to +** ORDER BY clause of the parent must be simple references to ** columns of the sub-query. ** -** (19) The subquery does not use LIMIT or the outer query does not +** (19) If the subquery uses LIMIT then the outer query may not ** have a WHERE clause. ** ** (20) If the sub-query is a compound select, then it must not use ** an ORDER BY clause. Ticket #3773. We could relax this constraint ** somewhat by saying that the terms of the ORDER BY clause must ** appear as unmodified result columns in the outer query. But we ** have other optimizations in mind to deal with that case. ** -** (21) The subquery does not use LIMIT or the outer query is not +** (21) If the subquery uses LIMIT then the outer query may not be ** DISTINCT. (See ticket [752e1646fc]). ** -** (22) The subquery is not a recursive CTE. +** (22) The subquery may not be a recursive CTE. ** -** (23) The parent is not a recursive CTE, or the sub-query is not a -** compound query. This restriction is because transforming the +** (23) If the outer query is a recursive CTE, then the sub-query may not be +** a compound query. This restriction is because transforming the ** parent to a compound query confuses the code that handles ** recursive queries in multiSelect(). ** -** (24) The subquery is not an aggregate that uses the built-in min() or +** (24) The subquery may not be an aggregate that uses the built-in min() or ** or max() functions. (Without this restriction, a query like: ** "SELECT x FROM (SELECT max(y), x FROM t1)" would not necessarily ** return the value X for which Y was maximal.) ** ** @@ -3433,11 +3436,11 @@ sqlite3 *db = pParse->db; /* Check to see if flattening is permitted. Return 0 if not. */ assert( p!=0 ); - assert( p->pPrior==0 ); /* Unable to flatten compound queries */ + assert( p->pPrior==0 ); if( OptimizationDisabled(db, SQLITE_QueryFlattener) ) return 0; pSrc = p->pSrc; assert( pSrc && iFrom>=0 && iFromnSrc ); pSubitem = &pSrc->a[iFrom]; iParent = pSubitem->iCursor; @@ -3465,11 +3468,11 @@ if( pSub->pOffset ) return 0; /* Restriction (14) */ if( (p->selFlags & SF_Compound)!=0 && pSub->pLimit ){ return 0; /* Restriction (15) */ } if( pSubSrc->nSrc==0 ) return 0; /* Restriction (7) */ - if( pSub->selFlags & SF_Distinct ) return 0; /* Restriction (5) */ + if( pSub->selFlags & SF_Distinct ) return 0; /* Restriction (4) */ if( pSub->pLimit && (pSrc->nSrc>1 || isAgg) ){ return 0; /* Restrictions (8)(9) */ } if( (p->selFlags & SF_Distinct)!=0 && subqueryIsAgg ){ return 0; /* Restriction (6) */ @@ -3491,11 +3494,12 @@ return 0; /* Restriction (23) */ } /* ** If the subquery is the right operand of a LEFT JOIN, then the - ** subquery may not be a join itself. Example of why this is not allowed: + ** subquery may not be a join itself (3a). Example of why this is not + ** allowed: ** ** t1 LEFT OUTER JOIN (t2 JOIN t3) ** ** If we flatten the above, we would get ** @@ -3502,20 +3506,21 @@ ** (t1 LEFT OUTER JOIN t2) JOIN t3 ** ** which is not at all the same thing. ** ** If the subquery is the right operand of a LEFT JOIN, then the outer - ** query cannot be an aggregate. This is an artifact of the way aggregates - ** are processed - there is no mechanism to determine if the LEFT JOIN - ** table should be all-NULL. + ** query cannot be an aggregate. (3c) This is an artifact of the way + ** aggregates are processed - there is no mechanism to determine if + ** the LEFT JOIN table should be all-NULL. ** ** See also tickets #306, #350, and #3300. */ if( (pSubitem->fg.jointype & JT_OUTER)!=0 ){ isLeftJoin = 1; if( pSubSrc->nSrc>1 || isAgg || IsVirtual(pSubSrc->a[0].pTab) ){ - return 0; /* Restriction (3) */ + /* (3a) (3c) (3b) */ + return 0; } } #ifdef SQLITE_EXTRA_IFNULLROW else if( iFrom>0 && !isAgg ){ /* Setting isLeftJoin to -1 causes OP_IfNullRow opcodes to be generated for @@ -3524,37 +3529,37 @@ ** opcode. */ isLeftJoin = -1; } #endif - /* Restriction 17: If the sub-query is a compound SELECT, then it must + /* Restriction (17): If the sub-query is a compound SELECT, then it must ** use only the UNION ALL operator. And none of the simple select queries ** that make up the compound SELECT are allowed to be aggregate or distinct ** queries. */ if( pSub->pPrior ){ if( pSub->pOrderBy ){ - return 0; /* Restriction 20 */ + return 0; /* Restriction (20) */ } if( isAgg || (p->selFlags & SF_Distinct)!=0 || pSrc->nSrc!=1 ){ - return 0; + return 0; /* (17d1), (17d2), or (17d3) */ } for(pSub1=pSub; pSub1; pSub1=pSub1->pPrior){ testcase( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct ); testcase( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))==SF_Aggregate ); assert( pSub->pSrc!=0 ); assert( pSub->pEList->nExpr==pSub1->pEList->nExpr ); - if( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))!=0 - || (pSub1->pPrior && pSub1->op!=TK_ALL) - || pSub1->pSrc->nSrc<1 + if( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))!=0 /* (17b) */ + || (pSub1->pPrior && pSub1->op!=TK_ALL) /* (17a) */ + || pSub1->pSrc->nSrc<1 /* (17c) */ ){ return 0; } testcase( pSub1->pSrc->nSrc>1 ); } - /* Restriction 18. */ + /* Restriction (18). */ if( p->pOrderBy ){ int ii; for(ii=0; iipOrderBy->nExpr; ii++){ if( p->pOrderBy->a[ii].u.x.iOrderByCol==0 ) return 0; }