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Improved processing of DISTINCT.

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FossilOrigin-Name: ba897100fed291d2025f68d09334f9985312298b
This commit is contained in:
drh
2013-06-11 18:59:38 +00:00
parent 8e23daf372
commit 4f402f26b1
5 changed files with 100 additions and 56 deletions
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126
src/where.c
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@@ -345,9 +345,11 @@ struct WhereInfo {
SrcList *pTabList; /* List of tables in the join */
ExprList *pOrderBy; /* The ORDER BY clause or NULL */
ExprList *pDistinct; /* DISTINCT ON values, or NULL */
WhereLoop *pLoops; /* List of all WhereLoop objects */
Bitmask revMask; /* Mask of ORDER BY terms that need reversing */
u16 nOBSat; /* Number of ORDER BY terms satisfied by indices */
WhereCost nRowOut; /* Estimated number of output rows */
u16 wctrlFlags; /* Flags originally passed to sqlite3WhereBegin() */
u8 bOBSat; /* ORDER BY satisfied by indices */
u8 okOnePass; /* Ok to use one-pass algorithm for UPDATE/DELETE */
u8 untestedTerms; /* Not all WHERE terms resolved by outer loop */
u8 eDistinct; /* One of the WHERE_DISTINCT_* values below */
@@ -355,11 +357,9 @@ struct WhereInfo {
int iContinue; /* Jump here to continue with next record */
int iBreak; /* Jump here to break out of the loop */
int nLevel; /* Number of nested loop */
int savedNQueryLoop; /* pParse->nQueryLoop outside the WHERE loop */
WhereMaskSet sMaskSet; /* Map cursor numbers to bitmasks */
WhereClause sWC; /* Decomposition of the WHERE clause */
WhereLoop *pLoops; /* List of all WhereLoop objects */
int savedNQueryLoop; /* pParse->nQueryLoop outside the WHERE loop */
WhereCost nRowOut; /* Estimated number of output rows */
WhereLevel a[1]; /* Information about each nest loop in WHERE */
};
@@ -441,7 +441,7 @@ int sqlite3WhereIsDistinct(WhereInfo *pWInfo){
** Return FALSE if the output needs to be sorted.
*/
int sqlite3WhereIsOrdered(WhereInfo *pWInfo){
return pWInfo->nOBSat>0;
return pWInfo->bOBSat!=0;
}
/*
@@ -1776,15 +1776,16 @@ static int findIndexCol(
/*
** Return true if the DISTINCT expression-list passed as the third argument
** is redundant. A DISTINCT list is redundant if the database contains a
** UNIQUE index that guarantees that the result of the query will be distinct
** anyway.
** is redundant.
**
** A DISTINCT list is redundant if the database contains some set of
** columns that are unique and non-null.
*/
static int isDistinctRedundant(
Parse *pParse,
SrcList *pTabList,
WhereClause *pWC,
ExprList *pDistinct
Parse *pParse, /* Parsing context */
SrcList *pTabList, /* The FROM clause */
WhereClause *pWC, /* The WHERE clause */
ExprList *pDistinct /* The result set that needs to be DISTINCT */
){
Table *pTab;
Index *pIdx;
@@ -3418,7 +3419,7 @@ static Bitmask codeOneLoopStart(
** this requires some special handling.
*/
if( (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN)!=0
&& (pWInfo->nOBSat>0)
&& (pWInfo->bOBSat!=0)
&& (pIdx->nColumn>nEq)
){
/* assert( pOrderBy->nExpr==1 ); */
@@ -4493,7 +4494,9 @@ static int whereLoopAddBtree(
){
pNew->iSortIdx = b ? iSortIdx : 0;
pNew->nOut = rSize;
pNew->rRun = whereCostAdd(rSize,rLogSize) + ((m==0 && b) ? 10 : 0);
pNew->rRun = whereCostAdd(rSize,rLogSize);
if( m!=0 ) pNew->rRun += rLogSize;
if( b ) pNew->rRun--;
rc = whereLoopInsert(pBuilder, pNew);
if( rc ) break;
}
@@ -4804,11 +4807,13 @@ static int whereLoopAddAll(WhereLoopBuilder *pBuilder){
*/
static int wherePathSatisfiesOrderBy(
WhereInfo *pWInfo, /* The WHERE clause */
ExprList *pOrderBy, /* ORDER BY or GROUP BY or DISTINCT clause to check */
WherePath *pPath, /* The WherePath to check */
int nLoop, /* Number of entries in pPath->aLoop[] */
int isLastLoop, /* True if pLast is the inner-most loop */
u16 wctrlFlags, /* Might contain WHERE_GROUPBY or WHERE_DISTINCTBY */
u16 nLoop, /* Number of entries in pPath->aLoop[] */
u8 isLastLoop, /* True if pLast is the inner-most loop */
WhereLoop *pLast, /* Add this WhereLoop to the end of pPath->aLoop[] */
Bitmask *pRevMask /* Mask of WhereLoops to run in reverse order */
Bitmask *pRevMask /* OUT: Mask of WhereLoops to run in reverse order */
){
u8 revSet; /* True if rev is known */
u8 rev; /* Composite sort order */
@@ -4823,7 +4828,6 @@ static int wherePathSatisfiesOrderBy(
int iCur; /* Cursor number for current WhereLoop */
int iColumn; /* A column number within table iCur */
WhereLoop *pLoop; /* Current WhereLoop being processed. */
ExprList *pOrderBy = pWInfo->pOrderBy; /* the ORDER BY clause */
WhereTerm *pTerm; /* A single term of the WHERE clause */
Expr *pOBExpr; /* An expression from the ORDER BY clause */
CollSeq *pColl; /* COLLATE function from an ORDER BY clause term */
@@ -4960,7 +4964,7 @@ static int wherePathSatisfiesOrderBy(
for(i=0; bOnce && i<nOrderBy; i++){
if( MASKBIT(i) & obSat ) continue;
pOBExpr = sqlite3ExprSkipCollate(pOrderBy->a[i].pExpr);
if( (pWInfo->wctrlFlags & WHERE_GROUPBY)==0 ) bOnce = 0;
if( (wctrlFlags & (WHERE_GROUPBY|WHERE_DISTINCTBY))==0 ) bOnce = 0;
if( pOBExpr->op!=TK_COLUMN ) continue;
if( pOBExpr->iTable!=iCur ) continue;
if( pOBExpr->iColumn!=iColumn ) continue;
@@ -5111,8 +5115,9 @@ static int wherePathSolver(WhereInfo *pWInfo, WhereCost nRowEst){
rCost = whereCostAdd(rCost, pFrom->rCost);
maskNew = pFrom->maskLoop | pWLoop->maskSelf;
if( !isOrderedValid ){
switch( wherePathSatisfiesOrderBy(pWInfo, pFrom, iLoop, iLoop==nLoop-1,
pWLoop, &revMask) ){
switch( wherePathSatisfiesOrderBy(pWInfo,
pWInfo->pOrderBy, pFrom, pWInfo->wctrlFlags,
iLoop, iLoop==nLoop-1, pWLoop, &revMask) ){
case 1: /* Yes. pFrom+pWLoop does satisfy the ORDER BY clause */
isOrdered = 1;
isOrderedValid = 1;
@@ -5249,9 +5254,22 @@ static int wherePathSolver(WhereInfo *pWInfo, WhereCost nRowEst){
pLevel->iFrom = pWLoop->iTab; /* FIXME: Omit the iFrom field */
pLevel->iTabCur = pWInfo->pTabList->a[pLevel->iFrom].iCursor;
}
if( (pWInfo->wctrlFlags & WHERE_DISTINCTBY)==0
&& pWInfo->pDistinct
&& nRowEst
){
Bitmask notUsed;
int rc = wherePathSatisfiesOrderBy(pWInfo, pWInfo->pDistinct, pFrom,
WHERE_DISTINCTBY, nLoop-1, 1, pFrom->aLoop[nLoop-1], &notUsed);
if( rc==1 ) pWInfo->eDistinct = WHERE_DISTINCT_ORDERED;
}
if( pFrom->isOrdered ){
pWInfo->nOBSat = pWInfo->pOrderBy->nExpr;
pWInfo->revMask = pFrom->revLoop;
if( pWInfo->wctrlFlags & WHERE_DISTINCTBY ){
pWInfo->eDistinct = WHERE_DISTINCT_ORDERED;
}else{
pWInfo->bOBSat = 1;
pWInfo->revMask = pFrom->revLoop;
}
}
pWInfo->nRowOut = pFrom->nRow;
@@ -5327,7 +5345,8 @@ static int whereShortCut(WhereLoopBuilder *pBuilder){
pLoop->maskSelf = getMask(&pWInfo->sMaskSet, iCur);
pWInfo->a[0].iTabCur = iCur;
pWInfo->nRowOut = 1;
pWInfo->nOBSat = pWInfo->pOrderBy ? pWInfo->pOrderBy->nExpr : 0;
if( pWInfo->pOrderBy ) pWInfo->bOBSat = 1;
if( pWInfo->pDistinct ) pWInfo->eDistinct = WHERE_DISTINCT_UNIQUE;
#ifdef SQLITE_DEBUG
pLoop->cId = '0';
#endif
@@ -5414,15 +5433,6 @@ static int whereShortCut(WhereLoopBuilder *pBuilder){
** pOrderBy is a pointer to the ORDER BY clause of a SELECT statement,
** if there is one. If there is no ORDER BY clause or if this routine
** is called from an UPDATE or DELETE statement, then pOrderBy is NULL.
**
** If an index can be used so that the natural output order of the table
** scan is correct for the ORDER BY clause, then that index is used and
** the returned WhereInfo.nOBSat field is set to pOrderBy->nExpr. This
** is an optimization that prevents an unnecessary sort of the result set
** if an index appropriate for the ORDER BY clause already exists.
**
** If the where clause loops cannot be arranged to provide the correct
** output order, then WhereInfo.nOBSat is 0.
*/
WhereInfo *sqlite3WhereBegin(
Parse *pParse, /* The parser context */
@@ -5558,13 +5568,32 @@ WhereInfo *sqlite3WhereBegin(
goto whereBeginError;
}
/* If the ORDER BY (or GROUP BY) clause contains references to general
** expressions, then we won't be able to satisfy it using indices, so
** go ahead and disable it now.
*/
if( pOrderBy ){
for(ii=0; ii<pOrderBy->nExpr; ii++){
Expr *pExpr = sqlite3ExprSkipCollate(pOrderBy->a[ii].pExpr);
if( pExpr->op!=TK_COLUMN ){
pWInfo->pOrderBy = pOrderBy = 0;
break;
}
}
}
/* Check if the DISTINCT qualifier, if there is one, is redundant.
** If it is, then set pDistinct to NULL and WhereInfo.eDistinct to
** WHERE_DISTINCT_UNIQUE to tell the caller to ignore the DISTINCT.
*/
if( pDistinct && isDistinctRedundant(pParse,pTabList,&pWInfo->sWC,pDistinct) ){
pDistinct = 0;
pWInfo->eDistinct = WHERE_DISTINCT_UNIQUE;
if( pDistinct ){
if( isDistinctRedundant(pParse,pTabList,&pWInfo->sWC,pDistinct) ){
pDistinct = 0;
pWInfo->eDistinct = WHERE_DISTINCT_UNIQUE;
}else if( pOrderBy==0 ){
pWInfo->wctrlFlags |= WHERE_DISTINCTBY;
pWInfo->pOrderBy = pDistinct;
}
}
/* Construct the WhereLoop objects */
@@ -5587,7 +5616,7 @@ WhereInfo *sqlite3WhereBegin(
}
#endif
wherePathSolver(pWInfo, -1);
wherePathSolver(pWInfo, 0);
if( db->mallocFailed ) goto whereBeginError;
if( pWInfo->pOrderBy ){
wherePathSolver(pWInfo, pWInfo->nRowOut);
@@ -5603,12 +5632,25 @@ WhereInfo *sqlite3WhereBegin(
#ifdef WHERETRACE_ENABLED
if( sqlite3WhereTrace ){
int ii;
sqlite3DebugPrintf("---- Solution");
if( pWInfo->nOBSat ){
sqlite3DebugPrintf(" ORDER BY omitted rev=0x%llx\n", pWInfo->revMask);
}else{
sqlite3DebugPrintf("\n");
sqlite3DebugPrintf("---- Solution nRow=%d", pWInfo->nRowOut);
if( pWInfo->bOBSat ){
sqlite3DebugPrintf(" ORDERBY=0x%llx", pWInfo->revMask);
}
switch( pWInfo->eDistinct ){
case WHERE_DISTINCT_UNIQUE: {
sqlite3DebugPrintf(" DISTINCT=unique");
break;
}
case WHERE_DISTINCT_ORDERED: {
sqlite3DebugPrintf(" DISTINCT=ordered");
break;
}
case WHERE_DISTINCT_UNORDERED: {
sqlite3DebugPrintf(" DISTINCT=unordered");
break;
}
}
sqlite3DebugPrintf("\n");
for(ii=0; ii<nTabList; ii++){
whereLoopPrint(pWInfo->a[ii].pWLoop, pTabList);
}