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Improved detection of unnecessary ORDER BY clauses.

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FossilOrigin-Name: 58805eb36b9975706e2c4e382689519454e9a504
This commit is contained in:
drh
2013-05-31 12:43:55 +00:00
parent 53b52f7f2e
commit d044d209f3
3 changed files with 29 additions and 20 deletions
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35
src/where.c
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@@ -3832,7 +3832,7 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
** is better and has fewer dependencies. Or the template will be ignored
** and no insert will occur if an existing WhereLoop is faster and has
** fewer dependencies than the template. Otherwise a new WhereLoop is
** added based no the template.
** added based on the template.
**
** If pBuilder->pBest is not NULL then we only care about the very
** best template and that template should be stored in pBuilder->pBest.
@@ -3848,6 +3848,8 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
** (2) They have the same iSortIdx.
** (3) The template has same or fewer dependencies than the current loop
** (4) The template has the same or lower cost than the current loop
** (5) The template uses more terms of the same index but has no additional
** dependencies
*/
static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
WhereLoop **ppPrev, *p, *pNext = 0, *pToFree = 0;
@@ -4100,7 +4102,7 @@ static int whereLoopAddBtree(
struct SrcList_item *pSrc; /* The FROM clause btree term to add */
WhereLoop *pNew; /* Template WhereLoop object */
int rc = SQLITE_OK; /* Return code */
int iSortIdx = 0; /* Index number */
int iSortIdx = 1; /* Index number */
int b; /* A boolean value */
double rSize; /* number of rows in the table */
double rLogSize; /* Logarithm of the number of rows in the table */
@@ -4179,6 +4181,7 @@ static int whereLoopAddBtree(
pNew->wsFlags = WHERE_IPK;
/* Full table scan */
pNew->iSortIdx = b ? iSortIdx : 0;
pNew->nOut = rSize;
pNew->rRun = (rSize + rLogSize)*(3+b); /* 4x penalty for a full-scan */
rc = whereLoopInsert(pBuilder, pNew);
@@ -4513,8 +4516,9 @@ static int wherePathSatisfiesOrderBy(
u8 revSet; /* True if rev is known */
u8 rev; /* Composite sort order */
u8 revIdx; /* Index sort order */
u8 isUnique;
u8 requireUnique = 0;
u8 isOneRow; /* Current WhereLoop is a one-row loop */
u8 requireOneRow = 0; /* All subsequent loops must be one-row */
u8 isUniqueIdx; /* Current WhereLoop uses a unique index */
u16 nColumn;
u16 nOrderBy;
int i, j;
@@ -4547,6 +4551,10 @@ static int wherePathSatisfiesOrderBy(
** of the index.
**
** (4) Index columns past nEq must match ORDER BY terms one-for-one.
**
** (5) If all columns of a UNIQUE index have been matched against ORDER BY
** terms, then any subsequent entries in the ORDER BY clause against the
** same table can be skipped.
*/
assert( pOrderBy!=0 );
@@ -4569,10 +4577,10 @@ static int wherePathSatisfiesOrderBy(
for(i=0; i<=nLoop && nUsed<nOrderBy; i++){
pLoop = i<nLoop ? pPath->aLoop[i] : pLast;
assert( (pLoop->wsFlags & WHERE_VIRTUALTABLE)==0 );
isUnique = 1;
isOneRow = isUniqueIdx = 1;
if( pLoop->wsFlags & WHERE_IPK ){
if( (pLoop->wsFlags & WHERE_COLUMN_IN)!=0 ) isUnique = 0;
if( pLoop->u.btree.nEq!=1 ) isUnique = 0;
if( (pLoop->wsFlags & WHERE_COLUMN_IN)!=0 ) isOneRow = 0;
if( pLoop->u.btree.nEq!=1 ) isOneRow = 0;
pIndex = 0;
nColumn = 0;
}else if( (pIndex = pLoop->u.btree.pIndex)==0 || pIndex->bUnordered ){
@@ -4580,16 +4588,16 @@ static int wherePathSatisfiesOrderBy(
}else{
nColumn = pIndex->nColumn;
if( pIndex->onError==OE_None ){
isUnique = 0;
isOneRow = isUniqueIdx = 0;
}else if( (pLoop->wsFlags & (WHERE_COLUMN_IN|WHERE_COLUMN_RANGE
|WHERE_COLUMN_NULL))!=0 ){
isUnique = 0;
isOneRow = 0;
}else if( pLoop->u.btree.nEq < pIndex->nColumn ){
isUnique = 0;
isOneRow = 0;
}
}
if( !isUnique && requireUnique ) return 0;
requireUnique = !isUnique;
if( !isOneRow && requireOneRow ) return 0;
requireOneRow = !isOneRow;
iCur = pWInfo->pTabList->a[pLoop->iTab].iCursor;
j = 0;
revSet = rev = 0;
@@ -4598,7 +4606,7 @@ static int wherePathSatisfiesOrderBy(
pOBExpr = sqlite3ExprSkipCollate(pOrderBy->a[nUsed].pExpr);
assert( pOBExpr->op==TK_COLUMN );
if( pOBExpr->iTable!=iCur ) break;
if( isUnique ) continue;
if( isOneRow ){ j--; continue; }
if( j<nColumn ){
/* Normal index columns */
iColumn = pIndex->aiColumn[j];
@@ -4629,6 +4637,7 @@ static int wherePathSatisfiesOrderBy(
revSet = 1;
}
}
if( j>=nColumn-1 && isUniqueIdx ){ j--; isOneRow = 1; }
}
if( rev ) revMask |= ((Bitmask)1)<<i;
}