Index: src/expr.c ================================================================== --- src/expr.c +++ src/expr.c @@ -3962,10 +3962,65 @@ ){ return 1; } return 0; } + +/* +** An instance of the following structure is used by the tree walker +** to determine if an expression can be evaluated by reference to the +** index only, without having to do a search for the corresponding +** table entry. The IdxCover.pIdx field is the index. IdxCover.iCur +** is the cursor for the table. +*/ +struct IdxCover { + Index *pIdx; /* The index to be tested for coverage */ + int iCur; /* Cursor number for the table corresponding to the index */ +}; + +/* +** Check to see if there are references to columns in table +** pWalker->u.pIdxCover->iCur can be satisfied using the index +** pWalker->u.pIdxCover->pIdx. +*/ +static int exprIdxCover(Walker *pWalker, Expr *pExpr){ + if( pExpr->op==TK_COLUMN + && pExpr->iTable==pWalker->u.pIdxCover->iCur + && sqlite3ColumnOfIndex(pWalker->u.pIdxCover->pIdx, pExpr->iColumn)<0 + ){ + pWalker->eCode = 1; + return WRC_Abort; + } + return WRC_Continue; +} + +/* +** Determine if an index on table iCur that contains the columns in +** Bitmask m will cover the expression pExpr. Return true if the index +** does cover the expression and false if the expression references +** table columns that are not found in the index. +** +** An index covering an expression means that the expression can be +** evaluated using only the index and without having to lookup the +** corresponding table entry. +*/ +int sqlite3ExprCoveredByIndex( + Expr *pExpr, /* The index to be tested */ + int iCur, /* The cursor number for the corresponding table */ + Index *pIdx /* The index that might be used for coverage */ +){ + Walker w; + struct IdxCover xcov; + memset(&w, 0, sizeof(w)); + xcov.iCur = iCur; + xcov.pIdx = pIdx; + w.xExprCallback = exprIdxCover; + w.u.pIdxCover = &xcov; + sqlite3WalkExpr(&w, pExpr); + return !w.eCode; +} + /* ** An instance of the following structure is used by the tree walker ** to count references to table columns in the arguments of an ** aggregate function, in order to implement the Index: src/sqliteInt.h ================================================================== --- src/sqliteInt.h +++ src/sqliteInt.h @@ -3255,10 +3255,11 @@ int iCur; /* A cursor number */ SrcList *pSrcList; /* FROM clause */ struct SrcCount *pSrcCount; /* Counting column references */ struct CCurHint *pCCurHint; /* Used by codeCursorHint() */ int *aiCol; /* array of column indexes */ + struct IdxCover *pIdxCover; /* Check for index coverage */ } u; }; /* Forward declarations */ int sqlite3WalkExpr(Walker*, Expr*); @@ -3698,10 +3699,11 @@ int sqlite3ExprCompare(Expr*, Expr*, int); int sqlite3ExprListCompare(ExprList*, ExprList*, int); int sqlite3ExprImpliesExpr(Expr*, Expr*, int); void sqlite3ExprAnalyzeAggregates(NameContext*, Expr*); void sqlite3ExprAnalyzeAggList(NameContext*,ExprList*); +int sqlite3ExprCoveredByIndex(Expr*, int iCur, Index *pIdx); int sqlite3FunctionUsesThisSrc(Expr*, SrcList*); Vdbe *sqlite3GetVdbe(Parse*); #ifndef SQLITE_OMIT_BUILTIN_TEST void sqlite3PrngSaveState(void); void sqlite3PrngRestoreState(void); Index: src/where.c ================================================================== --- src/where.c +++ src/where.c @@ -2773,15 +2773,38 @@ ){ pNew->iSortIdx = b ? iSortIdx : 0; /* The cost of visiting the index rows is N*K, where K is ** between 1.1 and 3.0, depending on the relative sizes of the - ** index and table rows. If this is a non-covering index scan, - ** also add the cost of visiting table rows (N*3.0). */ + ** index and table rows. */ pNew->rRun = rSize + 1 + (15*pProbe->szIdxRow)/pTab->szTabRow; if( m!=0 ){ - pNew->rRun = sqlite3LogEstAdd(pNew->rRun, rSize+16); + /* If this is a non-covering index scan, add in the cost of + ** doing table lookups. The cost will be 3x the number of + ** lookups. Take into account WHERE clause terms that can be + ** satisfied using just the index, and that do not require a + ** table lookup. */ + LogEst nLookup = rSize + 16; /* Base cost: N*3 */ + int ii; + int iCur = pSrc->iCursor; + WhereClause *pWC = &pWInfo->sWC; + for(ii=0; iinTerm; ii++){ + WhereTerm *pTerm = &pWC->a[ii]; + if( !sqlite3ExprCoveredByIndex(pTerm->pExpr, iCur, pProbe) ){ + break; + } + /* pTerm can be evaluated using just the index. So reduce + ** the expected number of table lookups accordingly */ + if( pTerm->truthProb<=0 ){ + nLookup += pTerm->truthProb; + }else{ + nLookup--; + if( pTerm->eOperator & (WO_EQ|WO_IS) ) nLookup -= 19; + } + } + + pNew->rRun = sqlite3LogEstAdd(pNew->rRun, nLookup); } ApplyCostMultiplier(pNew->rRun, pTab->costMult); whereLoopOutputAdjust(pWC, pNew, rSize); rc = whereLoopInsert(pBuilder, pNew); pNew->nOut = rSize;