** so is applicable. Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
-** $Id: where.c,v 1.338 2008/12/17 19:22:16 drh Exp $
+** $Id: where.c,v 1.339 2008/12/20 02:06:14 drh Exp $
*/
#include "sqliteInt.h"
*/
struct WhereOrInfo {
WhereClause wc; /* The OR subexpression broken out */
- double cost; /* Cost of evaluating this OR subexpression */
+ Bitmask indexable; /* Bitmask of all indexable tables in the clause */
};
/*
#define WO_AND 0x200 /* Two or more AND-connected terms */
#define WO_ALL 0xfff /* Mask of all possible WO_* values */
+#define WO_SINGLE 0x0ff /* Mask of all non-compound WO_* values */
/*
** Value for wsFlags returned by bestIndex() and stored in
static void whereOrInfoDelete(sqlite3 *db, WhereOrInfo *p){
if( p ){
whereClauseClear(&p->wc);
+ sqlite3DbFree(db, p);
}
}
static void whereAndInfoDelete(sqlite3 *db, WhereAndInfo *p){
if( p ){
whereClauseClear(&p->wc);
+ sqlite3DbFree(db, p);
}
}
#if !defined(SQLITE_OMIT_OR_OPTIMIZATION) && !defined(SQLITE_OMIT_SUBQUERY)
/*
-** Return TRUE if the given term of an OR clause can be converted
-** into an IN clause. The iCursor and iColumn define the left-hand
-** side of the IN clause.
+** Analyze a term that consists of two or more OR-connected
+** subterms. So in:
**
-** The context is that we have multiple OR-connected equality terms
-** like this:
+** ... WHERE (a=5) AND (b=7 OR c=9 OR d=13) AND (d=13)
+** ^^^^^^^^^^^^^^^^^^^^
**
-** a=<expr1> OR a=<expr2> OR b=<expr3> OR ...
+** This routine analyzes terms such as the middle term in the above example.
+** A WhereOrTerm object is computed and attached to the term under
+** analysis, regardless of the outcome of the analysis. Hence:
**
-** The pOrTerm input to this routine corresponds to a single term of
-** this OR clause. In order for the term to be a candidate for
-** conversion to an IN operator, the following must be true:
+** WhereTerm.wtFlags |= TERM_ORINFO
+** WhereTerm.u.pOrInfo = a dynamically allocated WhereOrTerm object
**
-** * The left-hand side of the term must be the column which
-** is identified by iCursor and iColumn.
+** The term being analyzed must have two or more of OR-connected subterms.
+** A single subterms might be a set of AND-connected sub-subterms.
+** Examples of terms under analysis:
**
-** * If the right-hand side is also a column, then the affinities
-** of both right and left sides must be such that no type
-** conversions are required on the right. (Ticket #2249)
+** (A) t1.x=t2.y OR t1.x=t2.z OR t1.y=15 OR t1.z=t3.a+5
+** (B) x=expr1 OR expr2=x OR x=expr3
+** (C) t1.x=t2.y OR (t1.x=t2.z AND t1.y=15)
+** (D) x=expr1 OR (y>11 AND y<22 AND z LIKE '*hello*')
+** (E) (p.a=1 AND q.b=2 AND r.c=3) OR (p.x=4 AND q.y=5 AND r.z=6)
**
-** If both of these conditions are true, then return true. Otherwise
-** return false.
-*/
-static int orTermIsOptCandidate(WhereTerm *pOrTerm, int iCursor, int iColumn){
- int affLeft, affRight;
- assert( pOrTerm->eOperator==WO_EQ );
- if( pOrTerm->leftCursor!=iCursor ){
- return 0;
- }
- if( pOrTerm->u.leftColumn!=iColumn ){
- return 0;
- }
- affRight = sqlite3ExprAffinity(pOrTerm->pExpr->pRight);
- if( affRight==0 ){
- return 1;
- }
- affLeft = sqlite3ExprAffinity(pOrTerm->pExpr->pLeft);
- if( affRight!=affLeft ){
- return 0;
- }
- return 1;
-}
-
-/*
-** Return true if the given term of an OR clause can be ignored during
-** a check to make sure all OR terms are candidates for optimization.
-** In other words, return true if a call to the orTermIsOptCandidate()
-** above returned false but it is not necessary to disqualify the
-** optimization.
+** CASE 1:
+**
+** If all subterms are of the form T.C=expr for some single column of C
+** a single table T (as shown in example B above) then create a new virtual
+** term that is an equivalent IN expression. In other words, if the term
+** being analyzed is:
**
-** Suppose the original OR phrase was this:
+** x = expr1 OR expr2 = x OR x = expr3
**
-** a=4 OR a=11 OR a=b
+** then create a new virtual term like this:
**
-** During analysis, the third term gets flipped around and duplicate
-** so that we are left with this:
+** x IN (expr1,expr2,expr3)
**
-** a=4 OR a=11 OR a=b OR b=a
+** CASE 2:
**
-** Since the last two terms are duplicates, only one of them
-** has to qualify in order for the whole phrase to qualify. When
-** this routine is called, we know that pOrTerm did not qualify.
-** This routine merely checks to see if pOrTerm has a duplicate that
-** might qualify. If there is a duplicate that has not yet been
-** disqualified, then return true. If there are no duplicates, or
-** the duplicate has also been disqualified, return false.
+** If all subterms are indexable by a single table T, then set
+**
+** WhereTerm.eOperator = WO_OR
+** WhereTerm.u.pOrInfo->indexable |= the cursor number for table T
+**
+** A subterm is "indexable" if it is of the form
+** "T.C <op> <expr>" where C is any column of table T and
+** <op> is one of "=", "<", "<=", ">", ">=", "IS NULL", or "IN".
+** A subterm is also indexable if it is an AND of two or more
+** subsubterms at least one of which is indexable. Indexable AND
+** subterms have their eOperator set to WO_AND and they have
+** u.pAndInfo set to a dynamically allocated WhereAndTerm object.
+**
+** From another point of view, "indexable" means that the subterm could
+** potentially be used with an index if an appropriate index exists.
+** This analysis does not consider whether or not the index exists; that
+** is something the bestIndex() routine will determine. This analysis
+** only looks at whether subterms appropriate for indexing exist.
+**
+** All examples A through E above all satisfy case 2. But if a term
+** also statisfies case 1 (such as B) we know that the optimizer will
+** always prefer case 1, so in that case we pretend that case 2 is not
+** satisfied.
+**
+** It might be the case that multiple tables are indexable. For example,
+** (E) above is indexable on tables P, Q, and R.
+**
+** Terms that satisfy case 2 are candidates for lookup by using
+** separate indices to find rowids for each subterm and composing
+** the union of all rowids using a RowSet object. This is similar
+** to "bitmap indices" in other database engines.
+**
+** OTHERWISE:
+**
+** If neither case 1 nor case 2 apply, then leave the eOperator set to
+** zero. This term is not useful for search.
*/
-static int orTermHasOkDuplicate(WhereClause *pOr, WhereTerm *pOrTerm){
- if( pOrTerm->wtFlags & TERM_COPIED ){
- /* This is the original term. The duplicate is to the left had
- ** has not yet been analyzed and thus has not yet been disqualified. */
- return 1;
+static void exprAnalyzeOrTerm(
+ SrcList *pSrc, /* the FROM clause */
+ WhereClause *pWC, /* the complete WHERE clause */
+ int idxTerm /* Index of the OR-term to be analyzed */
+){
+ Parse *pParse = pWC->pParse; /* Parser context */
+ sqlite3 *db = pParse->db; /* Database connection */
+ WhereTerm *pTerm = &pWC->a[idxTerm]; /* The term to be analyzed */
+ Expr *pExpr = pTerm->pExpr; /* The expression of the term */
+ ExprMaskSet *pMaskSet = pWC->pMaskSet; /* Table use masks */
+ int i; /* Loop counters */
+ WhereClause *pOrWc; /* Breakup of pTerm into subterms */
+ WhereTerm *pOrTerm; /* A Sub-term within the pOrWc */
+ WhereOrInfo *pOrInfo; /* Additional information associated with pTerm */
+ Bitmask chngToIN; /* Tables that might satisfy case 1 */
+ Bitmask indexable; /* Tables that are indexable, satisfying case 2 */
+
+ /*
+ ** Break the OR clause into its separate subterms. The subterms are
+ ** stored in a WhereClause structure containing within the WhereOrInfo
+ ** object that is attached to the original OR clause term.
+ */
+ assert( (pTerm->wtFlags & (TERM_DYNAMIC|TERM_ORINFO|TERM_ANDINFO))==0 );
+ assert( pExpr->op==TK_OR );
+ pTerm->u.pOrInfo = pOrInfo = sqlite3DbMallocRaw(db, sizeof(*pOrInfo));
+ if( pOrInfo==0 ) return;
+ pTerm->wtFlags |= TERM_ORINFO;
+ pOrWc = &pOrInfo->wc;
+ whereClauseInit(pOrWc, pWC->pParse, pMaskSet);
+ whereSplit(pOrWc, pExpr, TK_OR);
+ exprAnalyzeAll(pSrc, pOrWc);
+ if( db->mallocFailed ) return;
+ assert( pOrWc->nTerm>=2 );
+
+ /*
+ ** Compute the set of tables that might satisfy cases 1 or 2.
+ */
+ indexable = chngToIN = ~(Bitmask)0;
+ for(i=pOrWc->nTerm-1, pOrTerm=pOrWc->a; i>=0 && indexable; i--, pOrTerm++){
+ if( (pOrTerm->eOperator & WO_SINGLE)==0 ){
+ chngToIN = 0;
+ indexable = 0; /***** FIX ME. Some AND clauses are indexable. */
+ }else if( pOrTerm->wtFlags & TERM_COPIED ){
+ /* Skip this term for now. We revisit it when we process the
+ ** corresponding TERM_VIRTUAL term */
+ }else{
+ Bitmask b;
+ b = getMask(pMaskSet, pOrTerm->leftCursor);
+ if( pOrTerm->wtFlags & TERM_VIRTUAL ){
+ WhereTerm *pOther = &pOrWc->a[pOrTerm->iParent];
+ b |= getMask(pMaskSet, pOther->leftCursor);
+ }
+ indexable &= b;
+ if( pOrTerm->eOperator!=WO_EQ ){
+ chngToIN = 0;
+ }else{
+ chngToIN &= b;
+ }
+ }
}
- if( (pOrTerm->wtFlags & TERM_VIRTUAL)!=0
- && (pOr->a[pOrTerm->iParent].wtFlags & TERM_OR_OK)!=0 ){
- /* This is a duplicate term. The original qualified so this one
- ** does not have to. */
- return 1;
+
+ /*
+ ** Record the set of tables that satisfy case 2. The set might be
+ ** empty, but that is OK.
+ */
+ pOrInfo->indexable = indexable;
+ pTerm->eOperator = WO_OR;
+
+ /*
+ ** chngToIN holds a set of tables that *might* satisfy case 1. But
+ ** we have to do some additional checking to see if case 1 really
+ ** is satisfied.
+ */
+ if( chngToIN ){
+ int okToChngToIN = 0; /* True if the conversion to IN is valid */
+ int iColumn = -1; /* Column index on lhs of IN operator */
+ int iCursor; /* Table cursor common to all terms */
+ int j = 0; /* Loop counter */
+
+ /* Search for a table and column that appears on one side or the
+ ** other of the == operator in every subterm. That table and column
+ ** will be recorded in iCursor and iColumn. There might not be any
+ ** such table and column. Set okToChngToIN if an appropriate table
+ ** and column is found but leave okToChngToIN false if not found.
+ */
+ for(j=0; j<2 && !okToChngToIN; j++){
+ pOrTerm = pOrWc->a;
+ for(i=pOrWc->nTerm-1; i>=0; i--, pOrTerm++){
+ assert( pOrTerm->eOperator==WO_EQ );
+ pOrTerm->wtFlags &= ~TERM_OR_OK;
+ if( pOrTerm->leftCursor==iColumn ) continue;
+ if( (chngToIN & getMask(pMaskSet, pOrTerm->leftCursor))==0 ) continue;
+ iColumn = pOrTerm->u.leftColumn;
+ iCursor = pOrTerm->leftCursor;
+ break;
+ }
+ if( i<0 ){
+ assert( j==1 );
+ assert( (chngToIN&(chngToIN-1))==0 );
+ assert( chngToIN==getMask(pMaskSet, iColumn) );
+ break;
+ }
+ okToChngToIN = 1;
+ for(; i>=0 && okToChngToIN; i--, pOrTerm++){
+ assert( pOrTerm->eOperator==WO_EQ );
+ if( pOrTerm->leftCursor!=iCursor ){
+ pOrTerm->wtFlags &= ~TERM_OR_OK;
+ }else if( pOrTerm->u.leftColumn!=iColumn ){
+ okToChngToIN = 0;
+ }else{
+ int affLeft, affRight;
+ /* If the right-hand side is also a column, then the affinities
+ ** of both right and left sides must be such that no type
+ ** conversions are required on the right. (Ticket #2249)
+ */
+ affRight = sqlite3ExprAffinity(pOrTerm->pExpr->pRight);
+ affLeft = sqlite3ExprAffinity(pOrTerm->pExpr->pLeft);
+ if( affRight!=0 && affRight!=affLeft ){
+ okToChngToIN = 0;
+ }else{
+ pOrTerm->wtFlags |= TERM_OR_OK;
+ }
+ }
+ }
+ }
+
+ /* At this point, okToChngToIN is true if original pTerm satisfies
+ ** case 1. In that case, construct a new virtual term that is
+ ** pTerm converted into an IN operator.
+ */
+ if( okToChngToIN ){
+ Expr *pDup; /* A transient duplicate expression */
+ ExprList *pList = 0; /* The RHS of the IN operator */
+ Expr *pLeft = 0; /* The LHS of the IN operator */
+ Expr *pNew; /* The complete IN operator */
+
+ for(i=pOrWc->nTerm-1, pOrTerm=pOrWc->a; i>=0; i--, pOrTerm++){
+ if( (pOrTerm->wtFlags & TERM_OR_OK)==0 ) continue;
+ assert( pOrTerm->eOperator==WO_EQ );
+ assert( pOrTerm->leftCursor==iCursor );
+ assert( pOrTerm->u.leftColumn==iColumn );
+ pDup = sqlite3ExprDup(db, pOrTerm->pExpr->pRight);
+ pList = sqlite3ExprListAppend(pWC->pParse, pList, pDup, 0);
+ pLeft = pOrTerm->pExpr->pLeft;
+ }
+ assert( pLeft!=0 );
+ pDup = sqlite3ExprDup(db, pLeft);
+ pNew = sqlite3Expr(db, TK_IN, pDup, 0, 0);
+ if( pNew ){
+ int idxNew;
+ transferJoinMarkings(pNew, pExpr);
+ pNew->pList = pList;
+ idxNew = whereClauseInsert(pWC, pNew, TERM_VIRTUAL|TERM_DYNAMIC);
+ testcase( idxNew==0 );
+ exprAnalyze(pSrc, pWC, idxNew);
+ pTerm = &pWC->a[idxTerm];
+ pWC->a[idxNew].iParent = idxTerm;
+ pTerm->nChild = 1;
+ }else{
+ sqlite3ExprListDelete(db, pList);
+ }
+ pTerm->eOperator = 0; /* case 1 trumps case 2 */
+ }
}
- /* This is either a singleton term or else it is a duplicate for
- ** which the original did not qualify. Either way we are done for. */
- return 0;
}
#endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */
+
/*
** The input to this routine is an WhereTerm structure with only the
** "pExpr" field filled in. The job of this routine is to analyze the
** structure.
**
** If the expression is of the form "<expr> <op> X" it gets commuted
-** to the standard form of "X <op> <expr>". If the expression is of
-** the form "X <op> Y" where both X and Y are columns, then the original
-** expression is unchanged and a new virtual expression of the form
-** "Y <op> X" is added to the WHERE clause and analyzed separately.
+** to the standard form of "X <op> <expr>".
+**
+** If the expression is of the form "X <op> Y" where both X and Y are
+** columns, then the original expression is unchanged and a new virtual
+** term of the form "Y <op> X" is added to the WHERE clause and
+** analyzed separately. The original term is marked with TERM_COPIED
+** and the new term is marked with TERM_DYNAMIC (because it's pExpr
+** needs to be freed with the WhereClause) and TERM_VIRTUAL (because it
+** is a commuted copy of a prior term.) The original term has nChild=1
+** and the copy has idxParent set to the index of the original term.
*/
static void exprAnalyze(
SrcList *pSrc, /* the FROM clause */
WhereClause *pWC, /* the WHERE clause */
int idxTerm /* Index of the term to be analyzed */
){
- WhereTerm *pTerm;
- ExprMaskSet *pMaskSet;
- Expr *pExpr;
- Bitmask prereqLeft;
- Bitmask prereqAll;
+ WhereTerm *pTerm; /* The term to be analyzed */
+ ExprMaskSet *pMaskSet; /* Set of table index masks */
+ Expr *pExpr; /* The expression to be analyzed */
+ Bitmask prereqLeft; /* Prerequesites of the pExpr->pLeft */
+ Bitmask prereqAll; /* Prerequesites of pExpr */
Bitmask extraRight = 0;
int nPattern;
int isComplete;
int noCase;
- int op;
- Parse *pParse = pWC->pParse;
- sqlite3 *db = pParse->db;
+ int op; /* Top-level operator. pExpr->op */
+ Parse *pParse = pWC->pParse; /* Parsing context */
+ sqlite3 *db = pParse->db; /* Database connection */
if( db->mallocFailed ){
return;
#ifndef SQLITE_OMIT_BETWEEN_OPTIMIZATION
/* If a term is the BETWEEN operator, create two new virtual terms
- ** that define the range that the BETWEEN implements.
+ ** that define the range that the BETWEEN implements. For example:
+ **
+ ** a BETWEEN b AND c
+ **
+ ** is converted into:
+ **
+ ** (a BETWEEN b AND c) AND (a>=b) AND (a<=c)
+ **
+ ** The two new terms are added onto the end of the WhereClause object.
+ ** The new terms are "dynamic" and are children of the original BETWEEN
+ ** term. That means that if the BETWEEN term is coded, the children are
+ ** skipped. Or, if the children are satisfied by an index, the original
+ ** BETWEEN term is skipped.
*/
else if( pExpr->op==TK_BETWEEN ){
ExprList *pList = pExpr->pList;
#endif /* SQLITE_OMIT_BETWEEN_OPTIMIZATION */
#if !defined(SQLITE_OMIT_OR_OPTIMIZATION) && !defined(SQLITE_OMIT_SUBQUERY)
- /* Attempt to convert OR-connected terms into an IN operator so that
- ** they can make use of indices. Example:
- **
- ** x = expr1 OR expr2 = x OR x = expr3
- **
- ** is converted into
- **
- ** x IN (expr1,expr2,expr3)
- **
- ** This optimization must be omitted if OMIT_SUBQUERY is defined because
- ** the compiler for the the IN operator is part of sub-queries.
+ /* Analyze a term that is composed of two or more subterms connected by
+ ** an OR operator.
*/
else if( pExpr->op==TK_OR ){
- int ok;
- int i, j;
- int iColumn, iCursor;
- WhereClause sOr;
- WhereTerm *pOrTerm;
-
- assert( (pTerm->wtFlags & TERM_DYNAMIC)==0 );
- whereClauseInit(&sOr, pWC->pParse, pMaskSet);
- whereSplit(&sOr, pExpr, TK_OR);
- exprAnalyzeAll(pSrc, &sOr);
- assert( sOr.nTerm>=2 );
- j = 0;
- if( db->mallocFailed ) goto or_not_possible;
- do{
- assert( j<sOr.nTerm );
- iColumn = sOr.a[j].u.leftColumn;
- iCursor = sOr.a[j].leftCursor;
- ok = iCursor>=0;
- for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0 && ok; i--, pOrTerm++){
- if( pOrTerm->eOperator!=WO_EQ ){
- goto or_not_possible;
- }
- if( orTermIsOptCandidate(pOrTerm, iCursor, iColumn) ){
- pOrTerm->wtFlags |= TERM_OR_OK;
- }else if( orTermHasOkDuplicate(&sOr, pOrTerm) ){
- pOrTerm->wtFlags &= ~TERM_OR_OK;
- }else{
- ok = 0;
- }
- }
- }while( !ok && (sOr.a[j++].wtFlags & TERM_COPIED)!=0 && j<2 );
- if( ok ){
- ExprList *pList = 0;
- Expr *pNew, *pDup;
- Expr *pLeft = 0;
- for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0; i--, pOrTerm++){
- if( (pOrTerm->wtFlags & TERM_OR_OK)==0 ) continue;
- pDup = sqlite3ExprDup(db, pOrTerm->pExpr->pRight);
- pList = sqlite3ExprListAppend(pWC->pParse, pList, pDup, 0);
- pLeft = pOrTerm->pExpr->pLeft;
- }
- assert( pLeft!=0 );
- pDup = sqlite3ExprDup(db, pLeft);
- pNew = sqlite3Expr(db, TK_IN, pDup, 0, 0);
- if( pNew ){
- int idxNew;
- transferJoinMarkings(pNew, pExpr);
- pNew->pList = pList;
- idxNew = whereClauseInsert(pWC, pNew, TERM_VIRTUAL|TERM_DYNAMIC);
- testcase( idxNew==0 );
- exprAnalyze(pSrc, pWC, idxNew);
- pTerm = &pWC->a[idxTerm];
- pWC->a[idxNew].iParent = idxTerm;
- pTerm->nChild = 1;
- }else{
- sqlite3ExprListDelete(db, pList);
- }
- }
-or_not_possible:
- whereClauseClear(&sOr);
+ exprAnalyzeOrTerm(pSrc, pWC, idxTerm);
}
#endif /* SQLITE_OMIT_OR_OPTIMIZATION */
projects / thirdparty / sqlite.git / commitdiff
