Index: Makefile.in ================================================================== --- Makefile.in +++ Makefile.in @@ -166,11 +166,11 @@ # Object files for the SQLite library (non-amalgamation). # LIBOBJS0 = alter.lo analyze.lo attach.lo auth.lo \ backup.lo bitvec.lo btmutex.lo btree.lo build.lo \ callback.lo complete.lo ctime.lo date.lo dbstat.lo delete.lo \ - expr.lo fault.lo fkey.lo \ + expr.lo fault.lo fkey.lo flatten.lo \ fts3.lo fts3_aux.lo fts3_expr.lo fts3_hash.lo fts3_icu.lo \ fts3_porter.lo fts3_snippet.lo fts3_tokenizer.lo fts3_tokenizer1.lo \ fts3_tokenize_vtab.lo \ fts3_unicode.lo fts3_unicode2.lo fts3_write.lo \ func.lo global.lo hash.lo \ @@ -216,10 +216,11 @@ $(TOP)/src/dbstat.c \ $(TOP)/src/delete.c \ $(TOP)/src/expr.c \ $(TOP)/src/fault.c \ $(TOP)/src/fkey.c \ + $(TOP)/src/flatten.c \ $(TOP)/src/func.c \ $(TOP)/src/global.c \ $(TOP)/src/hash.c \ $(TOP)/src/hash.h \ $(TOP)/src/hwtime.h \ @@ -688,10 +689,13 @@ $(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/fault.c fkey.lo: $(TOP)/src/fkey.c $(HDR) $(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/fkey.c +flatten.lo: $(TOP)/src/flatten.c $(HDR) + $(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/flatten.c + func.lo: $(TOP)/src/func.c $(HDR) $(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/func.c global.lo: $(TOP)/src/global.c $(HDR) $(LTCOMPILE) $(TEMP_STORE) -c $(TOP)/src/global.c Index: Makefile.msc ================================================================== --- Makefile.msc +++ Makefile.msc @@ -821,11 +821,11 @@ # Object files for the SQLite library (non-amalgamation). # LIBOBJS0 = vdbe.lo parse.lo alter.lo analyze.lo attach.lo auth.lo \ backup.lo bitvec.lo btmutex.lo btree.lo build.lo \ callback.lo complete.lo ctime.lo date.lo dbstat.lo delete.lo \ - expr.lo fault.lo fkey.lo \ + expr.lo fault.lo fkey.lo flatten.lo \ fts3.lo fts3_aux.lo fts3_expr.lo fts3_hash.lo fts3_icu.lo \ fts3_porter.lo fts3_snippet.lo fts3_tokenizer.lo fts3_tokenizer1.lo \ fts3_tokenize_vtab.lo fts3_unicode.lo fts3_unicode2.lo fts3_write.lo \ func.lo global.lo hash.lo \ icu.lo insert.lo journal.lo legacy.lo loadext.lo \ @@ -881,10 +881,11 @@ $(TOP)\src\dbstat.c \ $(TOP)\src\delete.c \ $(TOP)\src\expr.c \ $(TOP)\src\fault.c \ $(TOP)\src\fkey.c \ + $(TOP)\src\flatten.c \ $(TOP)\src\func.c \ $(TOP)\src\global.c \ $(TOP)\src\hash.c \ $(TOP)\src\hash.h \ $(TOP)\src\hwtime.h \ @@ -1369,10 +1370,13 @@ $(LTCOMPILE) $(CORE_COMPILE_OPTS) -c $(TOP)\src\fault.c fkey.lo: $(TOP)\src\fkey.c $(HDR) $(LTCOMPILE) $(CORE_COMPILE_OPTS) -c $(TOP)\src\fkey.c +flatten.lo: $(TOP)\src\flatten.c $(HDR) + $(LTCOMPILE) $(CORE_COMPILE_OPTS) -c $(TOP)\src\flatten.c + func.lo: $(TOP)\src\func.c $(HDR) $(LTCOMPILE) $(CORE_COMPILE_OPTS) -c $(TOP)\src\func.c global.lo: $(TOP)\src\global.c $(HDR) $(LTCOMPILE) $(CORE_COMPILE_OPTS) -c $(TOP)\src\global.c Index: main.mk ================================================================== --- main.mk +++ main.mk @@ -51,11 +51,12 @@ # Object files for the SQLite library. # LIBOBJ+= vdbe.o parse.o \ alter.o analyze.o attach.o auth.o \ backup.o bitvec.o btmutex.o btree.o build.o \ - callback.o complete.o ctime.o date.o dbstat.o delete.o expr.o fault.o fkey.o \ + callback.o complete.o ctime.o date.o dbstat.o delete.o expr.o \ + fault.o fkey.o flatten.o \ fts3.o fts3_aux.o fts3_expr.o fts3_hash.o fts3_icu.o fts3_porter.o \ fts3_snippet.o fts3_tokenizer.o fts3_tokenizer1.o \ fts3_tokenize_vtab.o \ fts3_unicode.o fts3_unicode2.o \ fts3_write.o func.o global.o hash.o \ @@ -94,10 +95,11 @@ $(TOP)/src/dbstat.c \ $(TOP)/src/delete.c \ $(TOP)/src/expr.c \ $(TOP)/src/fault.c \ $(TOP)/src/fkey.c \ + $(TOP)/src/flatten.c \ $(TOP)/src/func.c \ $(TOP)/src/global.c \ $(TOP)/src/hash.c \ $(TOP)/src/hash.h \ $(TOP)/src/hwtime.h \ ADDED src/flatten.c Index: src/flatten.c ================================================================== --- /dev/null +++ src/flatten.c @@ -0,0 +1,662 @@ +/* +** 2015-06-01 +** +** The author disclaims copyright to this source code. In place of +** a legal notice, here is a blessing: +** +** May you do good and not evil. +** May you find forgiveness for yourself and forgive others. +** May you share freely, never taking more than you give. +** +************************************************************************* +** +** This file contains C code used to transform FROM-clause subqueries +** in ways that result in faster query evaluation. +*/ +#include "sqliteInt.h" + +#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) +/* Forward Declarations */ +static void substExprList(sqlite3*, ExprList*, int, ExprList*); +static void substSelect(sqlite3*, Select *, int, ExprList *); + +/* +** Scan through the expression pExpr. Replace every reference to +** a column in table number iTable with a copy of the iColumn-th +** entry in pEList. (But leave references to the ROWID column +** unchanged.) +** +** This routine is part of the flattening procedure. A subquery +** whose result set is defined by pEList appears as entry in the +** FROM clause of a SELECT such that the VDBE cursor assigned to that +** FORM clause entry is iTable. This routine make the necessary +** changes to pExpr so that it refers directly to the source table +** of the subquery rather the result set of the subquery. +*/ +static Expr *substExpr( + sqlite3 *db, /* Report malloc errors to this connection */ + Expr *pExpr, /* Expr in which substitution occurs */ + int iTable, /* Table to be substituted */ + ExprList *pEList /* Substitute expressions */ +){ + if( pExpr==0 ) return 0; + if( pExpr->op==TK_COLUMN && pExpr->iTable==iTable ){ + if( pExpr->iColumn<0 ){ + pExpr->op = TK_NULL; + }else{ + Expr *pNew; + assert( pEList!=0 && pExpr->iColumnnExpr ); + assert( pExpr->pLeft==0 && pExpr->pRight==0 ); + pNew = sqlite3ExprDup(db, pEList->a[pExpr->iColumn].pExpr, 0); + sqlite3ExprDelete(db, pExpr); + pExpr = pNew; + } + }else{ + pExpr->pLeft = substExpr(db, pExpr->pLeft, iTable, pEList); + pExpr->pRight = substExpr(db, pExpr->pRight, iTable, pEList); + if( ExprHasProperty(pExpr, EP_xIsSelect) ){ + substSelect(db, pExpr->x.pSelect, iTable, pEList); + }else{ + substExprList(db, pExpr->x.pList, iTable, pEList); + } + } + return pExpr; +} +static void substExprList( + sqlite3 *db, /* Report malloc errors here */ + ExprList *pList, /* List to scan and in which to make substitutes */ + int iTable, /* Table to be substituted */ + ExprList *pEList /* Substitute values */ +){ + int i; + if( pList==0 ) return; + for(i=0; inExpr; i++){ + pList->a[i].pExpr = substExpr(db, pList->a[i].pExpr, iTable, pEList); + } +} +static void substSelect( + sqlite3 *db, /* Report malloc errors here */ + Select *p, /* SELECT statement in which to make substitutions */ + int iTable, /* Table to be replaced */ + ExprList *pEList /* Substitute values */ +){ + SrcList *pSrc; + struct SrcList_item *pItem; + int i; + if( !p ) return; + substExprList(db, p->pEList, iTable, pEList); + substExprList(db, p->pGroupBy, iTable, pEList); + substExprList(db, p->pOrderBy, iTable, pEList); + p->pHaving = substExpr(db, p->pHaving, iTable, pEList); + p->pWhere = substExpr(db, p->pWhere, iTable, pEList); + substSelect(db, p->pPrior, iTable, pEList); + pSrc = p->pSrc; + assert( pSrc ); /* Even for (SELECT 1) we have: pSrc!=0 but pSrc->nSrc==0 */ + if( ALWAYS(pSrc) ){ + for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){ + substSelect(db, pItem->pSelect, iTable, pEList); + } + } +} + +/* +** This routine attempts to flatten subqueries as a performance optimization. +** This routine returns 1 if it makes changes and 0 if no flattening occurs. +** +** To understand the concept of flattening, consider the following +** query: +** +** SELECT a FROM (SELECT x+y AS a FROM t1 WHERE z<100) WHERE a>5 +** +** The default way of implementing this query is to execute the +** subquery first and store the results in a temporary table, then +** run the outer query on that temporary table. This requires two +** passes over the data. Furthermore, because the temporary table +** has no indices, the WHERE clause on the outer query cannot be +** optimized. +** +** This routine attempts to rewrite queries such as the above into +** a single flat select, like this: +** +** SELECT x+y AS a FROM t1 WHERE z<100 AND a>5 +** +** 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: +** +** (1) The subquery and the outer query do not both use 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.) +** +** (3) The subquery is not the right operand of a left outer join +** (Originally ticket #306. Strengthened by ticket #3300) +** +** (4) The subquery is not 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. +** +** (7) The subquery has a FROM clause. TODO: For subqueries without +** A FROM clause, consider adding a FROM close 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. +** +** (9) The subquery does not use LIMIT or the outer query does not use +** aggregates. +** +** (**) 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." +** +** (11) The subquery and the outer query do 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. +** +** (14) The subquery does not use OFFSET. +** +** (15) The outer query is not part of a compound select or the +** subquery does not have a LIMIT clause. +** (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 +** 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 +** +** 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 +** operators have an implied DISTINCT which is disallowed by +** restriction (4). +** +** Also, each component of the sub-query must return the same number +** of result columns. This is actually a requirement for any compound +** 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 +** columns of the sub-query. +** +** (19) The subquery does not use LIMIT or the outer query does 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 +** DISTINCT. (See ticket [752e1646fc]). +** +** (22) The subquery is not 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 +** 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 +** 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.) +** +** +** In this routine, the "p" parameter is a pointer to the outer query. +** The subquery is p->pSrc->a[iFrom]. isAgg is true if the outer query +** uses aggregates and subqueryIsAgg is true if the subquery uses aggregates. +** +** If flattening is not attempted, this routine is a no-op and returns 0. +** If flattening is attempted this routine returns 1. +** +** All of the expression analysis must occur on both the outer query and +** the subquery before this routine runs. +*/ +int sqlite3FlattenSubquery( + Parse *pParse, /* Parsing context */ + Select *p, /* The parent or outer SELECT statement */ + int iFrom, /* Index in p->pSrc->a[] of the inner subquery */ + int isAgg, /* True if outer SELECT uses aggregate functions */ + int subqueryIsAgg /* True if the subquery uses aggregate functions */ +){ + const char *zSavedAuthContext = pParse->zAuthContext; + Select *pParent; + Select *pSub; /* The inner query or "subquery" */ + Select *pSub1; /* Pointer to the rightmost select in sub-query */ + SrcList *pSrc; /* The FROM clause of the outer query */ + SrcList *pSubSrc; /* The FROM clause of the subquery */ + ExprList *pList; /* The result set of the outer query */ + int iParent; /* VDBE cursor number of the pSub result set temp table */ + int i; /* Loop counter */ + Expr *pWhere; /* The WHERE clause */ + struct SrcList_item *pSubitem; /* The subquery */ + 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 */ + if( OptimizationDisabled(db, SQLITE_QueryFlattener) ) return 0; + pSrc = p->pSrc; + assert( pSrc && iFrom>=0 && iFromnSrc ); + pSubitem = &pSrc->a[iFrom]; + iParent = pSubitem->iCursor; + pSub = pSubitem->pSelect; + assert( pSub!=0 ); + if( subqueryIsAgg ){ + if( isAgg ) return 0; /* Restriction (1) */ + if( pSrc->nSrc>1 ) return 0; /* Restriction (2a) */ + if( (p->pWhere && ExprHasProperty(p->pWhere,EP_Subquery)) + || (sqlite3ExprListFlags(p->pEList) & EP_Subquery)!=0 + || (sqlite3ExprListFlags(p->pOrderBy) & EP_Subquery)!=0 + ){ + return 0; /* Restriction (2b) */ + } + } + + pSubSrc = pSub->pSrc; + assert( pSubSrc ); + /* Prior to version 3.1.2, when LIMIT and OFFSET had to be simple constants, + ** not arbitrary expressions, we allowed some combining of LIMIT and OFFSET + ** because they could be computed at compile-time. But when LIMIT and OFFSET + ** became arbitrary expressions, we were forced to add restrictions (13) + ** and (14). */ + if( pSub->pLimit && p->pLimit ) return 0; /* Restriction (13) */ + 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->pLimit && (pSrc->nSrc>1 || isAgg) ){ + return 0; /* Restrictions (8)(9) */ + } + if( (p->selFlags & SF_Distinct)!=0 && subqueryIsAgg ){ + return 0; /* Restriction (6) */ + } + if( p->pOrderBy && pSub->pOrderBy ){ + return 0; /* Restriction (11) */ + } + if( isAgg && pSub->pOrderBy ) return 0; /* Restriction (16) */ + if( pSub->pLimit && p->pWhere ) return 0; /* Restriction (19) */ + if( pSub->pLimit && (p->selFlags & SF_Distinct)!=0 ){ + return 0; /* Restriction (21) */ + } + testcase( pSub->selFlags & SF_Recursive ); + testcase( pSub->selFlags & SF_MinMaxAgg ); + if( pSub->selFlags & (SF_Recursive|SF_MinMaxAgg) ){ + return 0; /* Restrictions (22) and (24) */ + } + if( (p->selFlags & SF_Recursive) && pSub->pPrior ){ + return 0; /* Restriction (23) */ + } + + /* OBSOLETE COMMENT 1: + ** Restriction 3: If the subquery is a join, make sure the subquery is + ** not used as the right operand of an outer join. Examples of why this + ** is not allowed: + ** + ** t1 LEFT OUTER JOIN (t2 JOIN t3) + ** + ** If we flatten the above, we would get + ** + ** (t1 LEFT OUTER JOIN t2) JOIN t3 + ** + ** which is not at all the same thing. + ** + ** OBSOLETE COMMENT 2: + ** Restriction 12: If the subquery is the right operand of a left outer + ** join, make sure the subquery has no WHERE clause. + ** An examples of why this is not allowed: + ** + ** t1 LEFT OUTER JOIN (SELECT * FROM t2 WHERE t2.x>0) + ** + ** If we flatten the above, we would get + ** + ** (t1 LEFT OUTER JOIN t2) WHERE t2.x>0 + ** + ** But the t2.x>0 test will always fail on a NULL row of t2, which + ** effectively converts the OUTER JOIN into an INNER JOIN. + ** + ** THIS OVERRIDES OBSOLETE COMMENTS 1 AND 2 ABOVE: + ** Ticket #3300 shows that flattening the right term of a LEFT JOIN + ** is fraught with danger. Best to avoid the whole thing. If the + ** subquery is the right term of a LEFT JOIN, then do not flatten. + */ + if( (pSubitem->jointype & JT_OUTER)!=0 ){ + return 0; + } + + /* 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 */ + } + if( isAgg || (p->selFlags & SF_Distinct)!=0 || pSrc->nSrc!=1 ){ + return 0; + } + 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 ); + if( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))!=0 + || (pSub1->pPrior && pSub1->op!=TK_ALL) + || pSub1->pSrc->nSrc<1 + || pSub->pEList->nExpr!=pSub1->pEList->nExpr + ){ + return 0; + } + testcase( pSub1->pSrc->nSrc>1 ); + } + + /* Restriction 18. */ + if( p->pOrderBy ){ + int ii; + for(ii=0; iipOrderBy->nExpr; ii++){ + if( p->pOrderBy->a[ii].u.x.iOrderByCol==0 ) return 0; + } + } + } + + /***** If we reach this point, flattening is permitted. *****/ + SELECTTRACE(1,pParse,p,("flatten %s.%p from term %d\n", + pSub->zSelName, pSub, iFrom)); + + /* Authorize the subquery */ + pParse->zAuthContext = pSubitem->zName; + TESTONLY(i =) sqlite3AuthCheck(pParse, SQLITE_SELECT, 0, 0, 0); + testcase( i==SQLITE_DENY ); + pParse->zAuthContext = zSavedAuthContext; + + /* If the sub-query is a compound SELECT statement, then (by restrictions + ** 17 and 18 above) it must be a UNION ALL and the parent query must + ** be of the form: + ** + ** SELECT FROM () + ** + ** followed by any ORDER BY, LIMIT and/or OFFSET clauses. This block + ** creates N-1 copies of the parent query without any ORDER BY, LIMIT or + ** OFFSET clauses and joins them to the left-hand-side of the original + ** using UNION ALL operators. In this case N is the number of simple + ** select statements in the compound sub-query. + ** + ** Example: + ** + ** SELECT a+1 FROM ( + ** SELECT x FROM tab + ** UNION ALL + ** SELECT y FROM tab + ** UNION ALL + ** SELECT abs(z*2) FROM tab2 + ** ) WHERE a!=5 ORDER BY 1 + ** + ** Transformed into: + ** + ** SELECT x+1 FROM tab WHERE x+1!=5 + ** UNION ALL + ** SELECT y+1 FROM tab WHERE y+1!=5 + ** UNION ALL + ** SELECT abs(z*2)+1 FROM tab2 WHERE abs(z*2)+1!=5 + ** ORDER BY 1 + ** + ** We call this the "compound-subquery flattening". + */ + for(pSub=pSub->pPrior; pSub; pSub=pSub->pPrior){ + Select *pNew; + ExprList *pOrderBy = p->pOrderBy; + Expr *pLimit = p->pLimit; + Expr *pOffset = p->pOffset; + Select *pPrior = p->pPrior; + p->pOrderBy = 0; + p->pSrc = 0; + p->pPrior = 0; + p->pLimit = 0; + p->pOffset = 0; + pNew = sqlite3SelectDup(db, p, 0); + sqlite3SelectSetName(pNew, pSub->zSelName); + p->pOffset = pOffset; + p->pLimit = pLimit; + p->pOrderBy = pOrderBy; + p->pSrc = pSrc; + p->op = TK_ALL; + if( pNew==0 ){ + p->pPrior = pPrior; + }else{ + pNew->pPrior = pPrior; + if( pPrior ) pPrior->pNext = pNew; + pNew->pNext = p; + p->pPrior = pNew; + SELECTTRACE(2,pParse,p, + ("compound-subquery flattener creates %s.%p as peer\n", + pNew->zSelName, pNew)); + } + if( db->mallocFailed ) return 1; + } + + /* Begin flattening the iFrom-th entry of the FROM clause + ** in the outer query. + */ + pSub = pSub1 = pSubitem->pSelect; + + /* Delete the transient table structure associated with the + ** subquery + */ + sqlite3DbFree(db, pSubitem->zDatabase); + sqlite3DbFree(db, pSubitem->zName); + sqlite3DbFree(db, pSubitem->zAlias); + pSubitem->zDatabase = 0; + pSubitem->zName = 0; + pSubitem->zAlias = 0; + pSubitem->pSelect = 0; + + /* Defer deleting the Table object associated with the + ** subquery until code generation is + ** complete, since there may still exist Expr.pTab entries that + ** refer to the subquery even after flattening. Ticket #3346. + ** + ** pSubitem->pTab is always non-NULL by test restrictions and tests above. + */ + if( ALWAYS(pSubitem->pTab!=0) ){ + Table *pTabToDel = pSubitem->pTab; + if( pTabToDel->nRef==1 ){ + Parse *pToplevel = sqlite3ParseToplevel(pParse); + pTabToDel->pNextZombie = pToplevel->pZombieTab; + pToplevel->pZombieTab = pTabToDel; + }else{ + pTabToDel->nRef--; + } + pSubitem->pTab = 0; + } + + /* The following loop runs once for each term in a compound-subquery + ** flattening (as described above). If we are doing a different kind + ** of flattening - a flattening other than a compound-subquery flattening - + ** then this loop only runs once. + ** + ** This loop moves all of the FROM elements of the subquery into the + ** the FROM clause of the outer query. Before doing this, remember + ** the cursor number for the original outer query FROM element in + ** iParent. The iParent cursor will never be used. Subsequent code + ** will scan expressions looking for iParent references and replace + ** those references with expressions that resolve to the subquery FROM + ** elements we are now copying in. + */ + for(pParent=p; pParent; pParent=pParent->pPrior, pSub=pSub->pPrior){ + int nSubSrc; + u8 jointype = 0; + pSubSrc = pSub->pSrc; /* FROM clause of subquery */ + nSubSrc = pSubSrc->nSrc; /* Number of terms in subquery FROM clause */ + pSrc = pParent->pSrc; /* FROM clause of the outer query */ + + if( pSrc ){ + assert( pParent==p ); /* First time through the loop */ + jointype = pSubitem->jointype; + }else{ + assert( pParent!=p ); /* 2nd and subsequent times through the loop */ + pSrc = pParent->pSrc = sqlite3SrcListAppend(db, 0, 0, 0); + if( pSrc==0 ){ + assert( db->mallocFailed ); + break; + } + } + + /* The subquery uses a single slot of the FROM clause of the outer + ** query. If the subquery has more than one element in its FROM clause, + ** then expand the outer query to make space for it to hold all elements + ** of the subquery. + ** + ** Example: + ** + ** SELECT * FROM tabA, (SELECT * FROM sub1, sub2), tabB; + ** + ** The outer query has 3 slots in its FROM clause. One slot of the + ** outer query (the middle slot) is used by the subquery. The next + ** block of code will expand the out query to 4 slots. The middle + ** slot is expanded to two slots in order to make space for the + ** two elements in the FROM clause of the subquery. + */ + if( nSubSrc>1 ){ + pParent->pSrc = pSrc = sqlite3SrcListEnlarge(db, pSrc, nSubSrc-1,iFrom+1); + if( db->mallocFailed ){ + break; + } + } + + /* Transfer the FROM clause terms from the subquery into the + ** outer query. + */ + for(i=0; ia[i+iFrom].pUsing); + pSrc->a[i+iFrom] = pSubSrc->a[i]; + memset(&pSubSrc->a[i], 0, sizeof(pSubSrc->a[i])); + } + pSrc->a[iFrom].jointype = jointype; + + /* Now begin substituting subquery result set expressions for + ** references to the iParent in the outer query. + ** + ** Example: + ** + ** SELECT a+5, b*10 FROM (SELECT x*3 AS a, y+10 AS b FROM t1) WHERE a>b; + ** \ \_____________ subquery __________/ / + ** \_____________________ outer query ______________________________/ + ** + ** We look at every expression in the outer query and every place we see + ** "a" we substitute "x*3" and every place we see "b" we substitute "y+10". + */ + pList = pParent->pEList; + for(i=0; inExpr; i++){ + if( pList->a[i].zName==0 ){ + char *zName = sqlite3DbStrDup(db, pList->a[i].zSpan); + sqlite3Dequote(zName); + pList->a[i].zName = zName; + } + } + substExprList(db, pParent->pEList, iParent, pSub->pEList); + if( isAgg ){ + substExprList(db, pParent->pGroupBy, iParent, pSub->pEList); + pParent->pHaving = substExpr(db, pParent->pHaving, iParent, pSub->pEList); + } + if( pSub->pOrderBy ){ + /* At this point, any non-zero iOrderByCol values indicate that the + ** ORDER BY column expression is identical to the iOrderByCol'th + ** expression returned by SELECT statement pSub. Since these values + ** do not necessarily correspond to columns in SELECT statement pParent, + ** zero them before transfering the ORDER BY clause. + ** + ** Not doing this may cause an error if a subsequent call to this + ** function attempts to flatten a compound sub-query into pParent + ** (the only way this can happen is if the compound sub-query is + ** currently part of pSub->pSrc). See ticket [d11a6e908f]. */ + ExprList *pOrderBy = pSub->pOrderBy; + for(i=0; inExpr; i++){ + pOrderBy->a[i].u.x.iOrderByCol = 0; + } + assert( pParent->pOrderBy==0 ); + assert( pSub->pPrior==0 ); + pParent->pOrderBy = pOrderBy; + pSub->pOrderBy = 0; + }else if( pParent->pOrderBy ){ + substExprList(db, pParent->pOrderBy, iParent, pSub->pEList); + } + if( pSub->pWhere ){ + pWhere = sqlite3ExprDup(db, pSub->pWhere, 0); + }else{ + pWhere = 0; + } + if( subqueryIsAgg ){ + assert( pParent->pHaving==0 ); + pParent->pHaving = pParent->pWhere; + pParent->pWhere = pWhere; + pParent->pHaving = substExpr(db, pParent->pHaving, iParent, pSub->pEList); + pParent->pHaving = sqlite3ExprAnd(db, pParent->pHaving, + sqlite3ExprDup(db, pSub->pHaving, 0)); + assert( pParent->pGroupBy==0 ); + pParent->pGroupBy = sqlite3ExprListDup(db, pSub->pGroupBy, 0); + }else{ + pParent->pWhere = substExpr(db, pParent->pWhere, iParent, pSub->pEList); + pParent->pWhere = sqlite3ExprAnd(db, pParent->pWhere, pWhere); + } + + /* The flattened query is distinct if either the inner or the + ** outer query is distinct. + */ + pParent->selFlags |= pSub->selFlags & SF_Distinct; + + /* + ** SELECT ... FROM (SELECT ... LIMIT a OFFSET b) LIMIT x OFFSET y; + ** + ** One is tempted to try to add a and b to combine the limits. But this + ** does not work if either limit is negative. + */ + if( pSub->pLimit ){ + pParent->pLimit = pSub->pLimit; + pSub->pLimit = 0; + } + } + + /* Finially, delete what is left of the subquery and return + ** success. + */ + sqlite3SelectDelete(db, pSub1); + +#if SELECTTRACE_ENABLED + if( sqlite3SelectTrace & 0x100 ){ + sqlite3DebugPrintf("After flattening:\n"); + sqlite3TreeViewSelect(0, p, 0); + } +#endif + + return 1; +} +#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */ Index: src/global.c ================================================================== --- src/global.c +++ src/global.c @@ -258,5 +258,12 @@ ** created by mkopcodeh.awk during compilation. Data is obtained ** from the comments following the "case OP_xxxx:" statements in ** the vdbe.c file. */ const unsigned char sqlite3OpcodeProperty[] = OPFLG_INITIALIZER; + +/* +** Enable or disable tracing of SELECT statement compilation. +*/ +#if SELECTTRACE_ENABLED +int sqlite3SelectTrace = 0; +#endif Index: src/select.c ================================================================== --- src/select.c +++ src/select.c @@ -11,24 +11,10 @@ ************************************************************************* ** This file contains C code routines that are called by the parser ** to handle SELECT statements in SQLite. */ #include "sqliteInt.h" - -/* -** Trace output macros -*/ -#if SELECTTRACE_ENABLED -/***/ int sqlite3SelectTrace = 0; -# define SELECTTRACE(K,P,S,X) \ - if(sqlite3SelectTrace&(K)) \ - sqlite3DebugPrintf("%*s%s.%p: ",(P)->nSelectIndent*2-2,"",(S)->zSelName,(S)),\ - sqlite3DebugPrintf X -#else -# define SELECTTRACE(K,P,S,X) -#endif - /* ** An instance of the following object is used to record information about ** how to process the DISTINCT keyword, to simplify passing that information ** into the selectInnerLoop() routine. @@ -3068,657 +3054,10 @@ explainComposite(pParse, p->op, iSub1, iSub2, 0); return pParse->nErr!=0; } #endif -#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) -/* Forward Declarations */ -static void substExprList(sqlite3*, ExprList*, int, ExprList*); -static void substSelect(sqlite3*, Select *, int, ExprList *); - -/* -** Scan through the expression pExpr. Replace every reference to -** a column in table number iTable with a copy of the iColumn-th -** entry in pEList. (But leave references to the ROWID column -** unchanged.) -** -** This routine is part of the flattening procedure. A subquery -** whose result set is defined by pEList appears as entry in the -** FROM clause of a SELECT such that the VDBE cursor assigned to that -** FORM clause entry is iTable. This routine make the necessary -** changes to pExpr so that it refers directly to the source table -** of the subquery rather the result set of the subquery. -*/ -static Expr *substExpr( - sqlite3 *db, /* Report malloc errors to this connection */ - Expr *pExpr, /* Expr in which substitution occurs */ - int iTable, /* Table to be substituted */ - ExprList *pEList /* Substitute expressions */ -){ - if( pExpr==0 ) return 0; - if( pExpr->op==TK_COLUMN && pExpr->iTable==iTable ){ - if( pExpr->iColumn<0 ){ - pExpr->op = TK_NULL; - }else{ - Expr *pNew; - assert( pEList!=0 && pExpr->iColumnnExpr ); - assert( pExpr->pLeft==0 && pExpr->pRight==0 ); - pNew = sqlite3ExprDup(db, pEList->a[pExpr->iColumn].pExpr, 0); - sqlite3ExprDelete(db, pExpr); - pExpr = pNew; - } - }else{ - pExpr->pLeft = substExpr(db, pExpr->pLeft, iTable, pEList); - pExpr->pRight = substExpr(db, pExpr->pRight, iTable, pEList); - if( ExprHasProperty(pExpr, EP_xIsSelect) ){ - substSelect(db, pExpr->x.pSelect, iTable, pEList); - }else{ - substExprList(db, pExpr->x.pList, iTable, pEList); - } - } - return pExpr; -} -static void substExprList( - sqlite3 *db, /* Report malloc errors here */ - ExprList *pList, /* List to scan and in which to make substitutes */ - int iTable, /* Table to be substituted */ - ExprList *pEList /* Substitute values */ -){ - int i; - if( pList==0 ) return; - for(i=0; inExpr; i++){ - pList->a[i].pExpr = substExpr(db, pList->a[i].pExpr, iTable, pEList); - } -} -static void substSelect( - sqlite3 *db, /* Report malloc errors here */ - Select *p, /* SELECT statement in which to make substitutions */ - int iTable, /* Table to be replaced */ - ExprList *pEList /* Substitute values */ -){ - SrcList *pSrc; - struct SrcList_item *pItem; - int i; - if( !p ) return; - substExprList(db, p->pEList, iTable, pEList); - substExprList(db, p->pGroupBy, iTable, pEList); - substExprList(db, p->pOrderBy, iTable, pEList); - p->pHaving = substExpr(db, p->pHaving, iTable, pEList); - p->pWhere = substExpr(db, p->pWhere, iTable, pEList); - substSelect(db, p->pPrior, iTable, pEList); - pSrc = p->pSrc; - assert( pSrc ); /* Even for (SELECT 1) we have: pSrc!=0 but pSrc->nSrc==0 */ - if( ALWAYS(pSrc) ){ - for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){ - substSelect(db, pItem->pSelect, iTable, pEList); - } - } -} -#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */ - -#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) -/* -** This routine attempts to flatten subqueries as a performance optimization. -** This routine returns 1 if it makes changes and 0 if no flattening occurs. -** -** To understand the concept of flattening, consider the following -** query: -** -** SELECT a FROM (SELECT x+y AS a FROM t1 WHERE z<100) WHERE a>5 -** -** The default way of implementing this query is to execute the -** subquery first and store the results in a temporary table, then -** run the outer query on that temporary table. This requires two -** passes over the data. Furthermore, because the temporary table -** has no indices, the WHERE clause on the outer query cannot be -** optimized. -** -** This routine attempts to rewrite queries such as the above into -** a single flat select, like this: -** -** SELECT x+y AS a FROM t1 WHERE z<100 AND a>5 -** -** 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: -** -** (1) The subquery and the outer query do not both use 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.) -** -** (3) The subquery is not the right operand of a left outer join -** (Originally ticket #306. Strengthened by ticket #3300) -** -** (4) The subquery is not 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. -** -** (7) The subquery has a FROM clause. TODO: For subqueries without -** A FROM clause, consider adding a FROM close 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. -** -** (9) The subquery does not use LIMIT or the outer query does not use -** aggregates. -** -** (**) 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." -** -** (11) The subquery and the outer query do 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. -** -** (14) The subquery does not use OFFSET. -** -** (15) The outer query is not part of a compound select or the -** subquery does not have a LIMIT clause. -** (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 -** 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 -** -** 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 -** operators have an implied DISTINCT which is disallowed by -** restriction (4). -** -** Also, each component of the sub-query must return the same number -** of result columns. This is actually a requirement for any compound -** 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 -** columns of the sub-query. -** -** (19) The subquery does not use LIMIT or the outer query does 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 -** DISTINCT. (See ticket [752e1646fc]). -** -** (22) The subquery is not 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 -** 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 -** 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.) -** -** -** In this routine, the "p" parameter is a pointer to the outer query. -** The subquery is p->pSrc->a[iFrom]. isAgg is true if the outer query -** uses aggregates and subqueryIsAgg is true if the subquery uses aggregates. -** -** If flattening is not attempted, this routine is a no-op and returns 0. -** If flattening is attempted this routine returns 1. -** -** All of the expression analysis must occur on both the outer query and -** the subquery before this routine runs. -*/ -static int flattenSubquery( - Parse *pParse, /* Parsing context */ - Select *p, /* The parent or outer SELECT statement */ - int iFrom, /* Index in p->pSrc->a[] of the inner subquery */ - int isAgg, /* True if outer SELECT uses aggregate functions */ - int subqueryIsAgg /* True if the subquery uses aggregate functions */ -){ - const char *zSavedAuthContext = pParse->zAuthContext; - Select *pParent; - Select *pSub; /* The inner query or "subquery" */ - Select *pSub1; /* Pointer to the rightmost select in sub-query */ - SrcList *pSrc; /* The FROM clause of the outer query */ - SrcList *pSubSrc; /* The FROM clause of the subquery */ - ExprList *pList; /* The result set of the outer query */ - int iParent; /* VDBE cursor number of the pSub result set temp table */ - int i; /* Loop counter */ - Expr *pWhere; /* The WHERE clause */ - struct SrcList_item *pSubitem; /* The subquery */ - 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 */ - if( OptimizationDisabled(db, SQLITE_QueryFlattener) ) return 0; - pSrc = p->pSrc; - assert( pSrc && iFrom>=0 && iFromnSrc ); - pSubitem = &pSrc->a[iFrom]; - iParent = pSubitem->iCursor; - pSub = pSubitem->pSelect; - assert( pSub!=0 ); - if( subqueryIsAgg ){ - if( isAgg ) return 0; /* Restriction (1) */ - if( pSrc->nSrc>1 ) return 0; /* Restriction (2a) */ - if( (p->pWhere && ExprHasProperty(p->pWhere,EP_Subquery)) - || (sqlite3ExprListFlags(p->pEList) & EP_Subquery)!=0 - || (sqlite3ExprListFlags(p->pOrderBy) & EP_Subquery)!=0 - ){ - return 0; /* Restriction (2b) */ - } - } - - pSubSrc = pSub->pSrc; - assert( pSubSrc ); - /* Prior to version 3.1.2, when LIMIT and OFFSET had to be simple constants, - ** not arbitrary expressions, we allowed some combining of LIMIT and OFFSET - ** because they could be computed at compile-time. But when LIMIT and OFFSET - ** became arbitrary expressions, we were forced to add restrictions (13) - ** and (14). */ - if( pSub->pLimit && p->pLimit ) return 0; /* Restriction (13) */ - 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->pLimit && (pSrc->nSrc>1 || isAgg) ){ - return 0; /* Restrictions (8)(9) */ - } - if( (p->selFlags & SF_Distinct)!=0 && subqueryIsAgg ){ - return 0; /* Restriction (6) */ - } - if( p->pOrderBy && pSub->pOrderBy ){ - return 0; /* Restriction (11) */ - } - if( isAgg && pSub->pOrderBy ) return 0; /* Restriction (16) */ - if( pSub->pLimit && p->pWhere ) return 0; /* Restriction (19) */ - if( pSub->pLimit && (p->selFlags & SF_Distinct)!=0 ){ - return 0; /* Restriction (21) */ - } - testcase( pSub->selFlags & SF_Recursive ); - testcase( pSub->selFlags & SF_MinMaxAgg ); - if( pSub->selFlags & (SF_Recursive|SF_MinMaxAgg) ){ - return 0; /* Restrictions (22) and (24) */ - } - if( (p->selFlags & SF_Recursive) && pSub->pPrior ){ - return 0; /* Restriction (23) */ - } - - /* OBSOLETE COMMENT 1: - ** Restriction 3: If the subquery is a join, make sure the subquery is - ** not used as the right operand of an outer join. Examples of why this - ** is not allowed: - ** - ** t1 LEFT OUTER JOIN (t2 JOIN t3) - ** - ** If we flatten the above, we would get - ** - ** (t1 LEFT OUTER JOIN t2) JOIN t3 - ** - ** which is not at all the same thing. - ** - ** OBSOLETE COMMENT 2: - ** Restriction 12: If the subquery is the right operand of a left outer - ** join, make sure the subquery has no WHERE clause. - ** An examples of why this is not allowed: - ** - ** t1 LEFT OUTER JOIN (SELECT * FROM t2 WHERE t2.x>0) - ** - ** If we flatten the above, we would get - ** - ** (t1 LEFT OUTER JOIN t2) WHERE t2.x>0 - ** - ** But the t2.x>0 test will always fail on a NULL row of t2, which - ** effectively converts the OUTER JOIN into an INNER JOIN. - ** - ** THIS OVERRIDES OBSOLETE COMMENTS 1 AND 2 ABOVE: - ** Ticket #3300 shows that flattening the right term of a LEFT JOIN - ** is fraught with danger. Best to avoid the whole thing. If the - ** subquery is the right term of a LEFT JOIN, then do not flatten. - */ - if( (pSubitem->jointype & JT_OUTER)!=0 ){ - return 0; - } - - /* 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 */ - } - if( isAgg || (p->selFlags & SF_Distinct)!=0 || pSrc->nSrc!=1 ){ - return 0; - } - 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 ); - if( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))!=0 - || (pSub1->pPrior && pSub1->op!=TK_ALL) - || pSub1->pSrc->nSrc<1 - || pSub->pEList->nExpr!=pSub1->pEList->nExpr - ){ - return 0; - } - testcase( pSub1->pSrc->nSrc>1 ); - } - - /* Restriction 18. */ - if( p->pOrderBy ){ - int ii; - for(ii=0; iipOrderBy->nExpr; ii++){ - if( p->pOrderBy->a[ii].u.x.iOrderByCol==0 ) return 0; - } - } - } - - /***** If we reach this point, flattening is permitted. *****/ - SELECTTRACE(1,pParse,p,("flatten %s.%p from term %d\n", - pSub->zSelName, pSub, iFrom)); - - /* Authorize the subquery */ - pParse->zAuthContext = pSubitem->zName; - TESTONLY(i =) sqlite3AuthCheck(pParse, SQLITE_SELECT, 0, 0, 0); - testcase( i==SQLITE_DENY ); - pParse->zAuthContext = zSavedAuthContext; - - /* If the sub-query is a compound SELECT statement, then (by restrictions - ** 17 and 18 above) it must be a UNION ALL and the parent query must - ** be of the form: - ** - ** SELECT FROM () - ** - ** followed by any ORDER BY, LIMIT and/or OFFSET clauses. This block - ** creates N-1 copies of the parent query without any ORDER BY, LIMIT or - ** OFFSET clauses and joins them to the left-hand-side of the original - ** using UNION ALL operators. In this case N is the number of simple - ** select statements in the compound sub-query. - ** - ** Example: - ** - ** SELECT a+1 FROM ( - ** SELECT x FROM tab - ** UNION ALL - ** SELECT y FROM tab - ** UNION ALL - ** SELECT abs(z*2) FROM tab2 - ** ) WHERE a!=5 ORDER BY 1 - ** - ** Transformed into: - ** - ** SELECT x+1 FROM tab WHERE x+1!=5 - ** UNION ALL - ** SELECT y+1 FROM tab WHERE y+1!=5 - ** UNION ALL - ** SELECT abs(z*2)+1 FROM tab2 WHERE abs(z*2)+1!=5 - ** ORDER BY 1 - ** - ** We call this the "compound-subquery flattening". - */ - for(pSub=pSub->pPrior; pSub; pSub=pSub->pPrior){ - Select *pNew; - ExprList *pOrderBy = p->pOrderBy; - Expr *pLimit = p->pLimit; - Expr *pOffset = p->pOffset; - Select *pPrior = p->pPrior; - p->pOrderBy = 0; - p->pSrc = 0; - p->pPrior = 0; - p->pLimit = 0; - p->pOffset = 0; - pNew = sqlite3SelectDup(db, p, 0); - sqlite3SelectSetName(pNew, pSub->zSelName); - p->pOffset = pOffset; - p->pLimit = pLimit; - p->pOrderBy = pOrderBy; - p->pSrc = pSrc; - p->op = TK_ALL; - if( pNew==0 ){ - p->pPrior = pPrior; - }else{ - pNew->pPrior = pPrior; - if( pPrior ) pPrior->pNext = pNew; - pNew->pNext = p; - p->pPrior = pNew; - SELECTTRACE(2,pParse,p, - ("compound-subquery flattener creates %s.%p as peer\n", - pNew->zSelName, pNew)); - } - if( db->mallocFailed ) return 1; - } - - /* Begin flattening the iFrom-th entry of the FROM clause - ** in the outer query. - */ - pSub = pSub1 = pSubitem->pSelect; - - /* Delete the transient table structure associated with the - ** subquery - */ - sqlite3DbFree(db, pSubitem->zDatabase); - sqlite3DbFree(db, pSubitem->zName); - sqlite3DbFree(db, pSubitem->zAlias); - pSubitem->zDatabase = 0; - pSubitem->zName = 0; - pSubitem->zAlias = 0; - pSubitem->pSelect = 0; - - /* Defer deleting the Table object associated with the - ** subquery until code generation is - ** complete, since there may still exist Expr.pTab entries that - ** refer to the subquery even after flattening. Ticket #3346. - ** - ** pSubitem->pTab is always non-NULL by test restrictions and tests above. - */ - if( ALWAYS(pSubitem->pTab!=0) ){ - Table *pTabToDel = pSubitem->pTab; - if( pTabToDel->nRef==1 ){ - Parse *pToplevel = sqlite3ParseToplevel(pParse); - pTabToDel->pNextZombie = pToplevel->pZombieTab; - pToplevel->pZombieTab = pTabToDel; - }else{ - pTabToDel->nRef--; - } - pSubitem->pTab = 0; - } - - /* The following loop runs once for each term in a compound-subquery - ** flattening (as described above). If we are doing a different kind - ** of flattening - a flattening other than a compound-subquery flattening - - ** then this loop only runs once. - ** - ** This loop moves all of the FROM elements of the subquery into the - ** the FROM clause of the outer query. Before doing this, remember - ** the cursor number for the original outer query FROM element in - ** iParent. The iParent cursor will never be used. Subsequent code - ** will scan expressions looking for iParent references and replace - ** those references with expressions that resolve to the subquery FROM - ** elements we are now copying in. - */ - for(pParent=p; pParent; pParent=pParent->pPrior, pSub=pSub->pPrior){ - int nSubSrc; - u8 jointype = 0; - pSubSrc = pSub->pSrc; /* FROM clause of subquery */ - nSubSrc = pSubSrc->nSrc; /* Number of terms in subquery FROM clause */ - pSrc = pParent->pSrc; /* FROM clause of the outer query */ - - if( pSrc ){ - assert( pParent==p ); /* First time through the loop */ - jointype = pSubitem->jointype; - }else{ - assert( pParent!=p ); /* 2nd and subsequent times through the loop */ - pSrc = pParent->pSrc = sqlite3SrcListAppend(db, 0, 0, 0); - if( pSrc==0 ){ - assert( db->mallocFailed ); - break; - } - } - - /* The subquery uses a single slot of the FROM clause of the outer - ** query. If the subquery has more than one element in its FROM clause, - ** then expand the outer query to make space for it to hold all elements - ** of the subquery. - ** - ** Example: - ** - ** SELECT * FROM tabA, (SELECT * FROM sub1, sub2), tabB; - ** - ** The outer query has 3 slots in its FROM clause. One slot of the - ** outer query (the middle slot) is used by the subquery. The next - ** block of code will expand the out query to 4 slots. The middle - ** slot is expanded to two slots in order to make space for the - ** two elements in the FROM clause of the subquery. - */ - if( nSubSrc>1 ){ - pParent->pSrc = pSrc = sqlite3SrcListEnlarge(db, pSrc, nSubSrc-1,iFrom+1); - if( db->mallocFailed ){ - break; - } - } - - /* Transfer the FROM clause terms from the subquery into the - ** outer query. - */ - for(i=0; ia[i+iFrom].pUsing); - pSrc->a[i+iFrom] = pSubSrc->a[i]; - memset(&pSubSrc->a[i], 0, sizeof(pSubSrc->a[i])); - } - pSrc->a[iFrom].jointype = jointype; - - /* Now begin substituting subquery result set expressions for - ** references to the iParent in the outer query. - ** - ** Example: - ** - ** SELECT a+5, b*10 FROM (SELECT x*3 AS a, y+10 AS b FROM t1) WHERE a>b; - ** \ \_____________ subquery __________/ / - ** \_____________________ outer query ______________________________/ - ** - ** We look at every expression in the outer query and every place we see - ** "a" we substitute "x*3" and every place we see "b" we substitute "y+10". - */ - pList = pParent->pEList; - for(i=0; inExpr; i++){ - if( pList->a[i].zName==0 ){ - char *zName = sqlite3DbStrDup(db, pList->a[i].zSpan); - sqlite3Dequote(zName); - pList->a[i].zName = zName; - } - } - substExprList(db, pParent->pEList, iParent, pSub->pEList); - if( isAgg ){ - substExprList(db, pParent->pGroupBy, iParent, pSub->pEList); - pParent->pHaving = substExpr(db, pParent->pHaving, iParent, pSub->pEList); - } - if( pSub->pOrderBy ){ - /* At this point, any non-zero iOrderByCol values indicate that the - ** ORDER BY column expression is identical to the iOrderByCol'th - ** expression returned by SELECT statement pSub. Since these values - ** do not necessarily correspond to columns in SELECT statement pParent, - ** zero them before transfering the ORDER BY clause. - ** - ** Not doing this may cause an error if a subsequent call to this - ** function attempts to flatten a compound sub-query into pParent - ** (the only way this can happen is if the compound sub-query is - ** currently part of pSub->pSrc). See ticket [d11a6e908f]. */ - ExprList *pOrderBy = pSub->pOrderBy; - for(i=0; inExpr; i++){ - pOrderBy->a[i].u.x.iOrderByCol = 0; - } - assert( pParent->pOrderBy==0 ); - assert( pSub->pPrior==0 ); - pParent->pOrderBy = pOrderBy; - pSub->pOrderBy = 0; - }else if( pParent->pOrderBy ){ - substExprList(db, pParent->pOrderBy, iParent, pSub->pEList); - } - if( pSub->pWhere ){ - pWhere = sqlite3ExprDup(db, pSub->pWhere, 0); - }else{ - pWhere = 0; - } - if( subqueryIsAgg ){ - assert( pParent->pHaving==0 ); - pParent->pHaving = pParent->pWhere; - pParent->pWhere = pWhere; - pParent->pHaving = substExpr(db, pParent->pHaving, iParent, pSub->pEList); - pParent->pHaving = sqlite3ExprAnd(db, pParent->pHaving, - sqlite3ExprDup(db, pSub->pHaving, 0)); - assert( pParent->pGroupBy==0 ); - pParent->pGroupBy = sqlite3ExprListDup(db, pSub->pGroupBy, 0); - }else{ - pParent->pWhere = substExpr(db, pParent->pWhere, iParent, pSub->pEList); - pParent->pWhere = sqlite3ExprAnd(db, pParent->pWhere, pWhere); - } - - /* The flattened query is distinct if either the inner or the - ** outer query is distinct. - */ - pParent->selFlags |= pSub->selFlags & SF_Distinct; - - /* - ** SELECT ... FROM (SELECT ... LIMIT a OFFSET b) LIMIT x OFFSET y; - ** - ** One is tempted to try to add a and b to combine the limits. But this - ** does not work if either limit is negative. - */ - if( pSub->pLimit ){ - pParent->pLimit = pSub->pLimit; - pSub->pLimit = 0; - } - } - - /* Finially, delete what is left of the subquery and return - ** success. - */ - sqlite3SelectDelete(db, pSub1); - -#if SELECTTRACE_ENABLED - if( sqlite3SelectTrace & 0x100 ){ - sqlite3DebugPrintf("After flattening:\n"); - sqlite3TreeViewSelect(0, p, 0); - } -#endif - - return 1; -} -#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */ /* ** Based on the contents of the AggInfo structure indicated by the first ** argument, this function checks if the following are true: ** @@ -4807,11 +4146,11 @@ ** an exact limit. */ pParse->nHeight += sqlite3SelectExprHeight(p); isAggSub = (pSub->selFlags & SF_Aggregate)!=0; - if( flattenSubquery(pParse, p, i, isAgg, isAggSub) ){ + if( sqlite3FlattenSubquery(pParse, p, i, isAgg, isAggSub) ){ /* This subquery can be absorbed into its parent. */ if( isAggSub ){ isAgg = 1; p->selFlags |= SF_Aggregate; } Index: src/sqliteInt.h ================================================================== --- src/sqliteInt.h +++ src/sqliteInt.h @@ -770,10 +770,20 @@ #if defined(SQLITE_DEBUG) || defined(SQLITE_ENABLE_SELECTTRACE) # define SELECTTRACE_ENABLED 1 #else # define SELECTTRACE_ENABLED 0 #endif +#if SELECTTRACE_ENABLED +extern int sqlite3SelectTrace; /* Defined in global.c */ +# define SELECTTRACE(K,P,S,X) \ + if(sqlite3SelectTrace&(K)) \ + sqlite3DebugPrintf("%*s%s.%p: ",\ + (P)->nSelectIndent*2-2,"",(S)->zSelName,(S)),\ + sqlite3DebugPrintf X +#else +# define SELECTTRACE(K,P,S,X) +#endif /* ** An instance of the following structure is used to store the busy-handler ** callback for a given sqlite handle. ** @@ -3287,10 +3297,19 @@ void sqlite3SrcListDelete(sqlite3*, SrcList*); Index *sqlite3AllocateIndexObject(sqlite3*,i16,int,char**); Index *sqlite3CreateIndex(Parse*,Token*,Token*,SrcList*,ExprList*,int,Token*, Expr*, int, int); void sqlite3DropIndex(Parse*, SrcList*, int); +#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) +int sqlite3FlattenSubquery( + Parse *pParse, /* Parsing context */ + Select *p, /* The parent or outer SELECT statement */ + int iFrom, /* Index in p->pSrc->a[] of the inner subquery */ + int isAgg, /* True if outer SELECT uses aggregate functions */ + int subqueryIsAgg /* True if the subquery uses aggregate functions */ +); +#endif int sqlite3Select(Parse*, Select*, SelectDest*); Select *sqlite3SelectNew(Parse*,ExprList*,SrcList*,Expr*,ExprList*, Expr*,ExprList*,u16,Expr*,Expr*); void sqlite3SelectDelete(sqlite3*, Select*); Table *sqlite3SrcListLookup(Parse*, SrcList*); Index: tool/mksqlite3c.tcl ================================================================== --- tool/mksqlite3c.tcl +++ tool/mksqlite3c.tcl @@ -335,10 +335,11 @@ insert.c legacy.c loadext.c pragma.c prepare.c + flatten.c select.c table.c trigger.c update.c vacuum.c