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The WHERE-clause constant propagation optimization attempts to use

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transitive laws to replace column values with constants in the WHERE
clause in order to help to query planner make more aggressive optimizations.

FossilOrigin-Name: f4229707ac08d66c5b0f53483ce17a63f5ac40a21922f66c3408e1b6fda3a7c2
This commit is contained in:
drh
2018-07-27 20:37:42 +00:00
parent ce705305b5 9cbf4f3550
commit 2d475e80bd
11 changed files with 304 additions and 31 deletions
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27
src/expr.c
View File

@@ -141,14 +141,6 @@ CollSeq *sqlite3ExprCollSeq(Parse *pParse, Expr *pExpr){
while( p ){
int op = p->op;
if( p->flags & EP_Generic ) break;
if( op==TK_CAST || op==TK_UPLUS ){
p = p->pLeft;
continue;
}
if( op==TK_COLLATE || (op==TK_REGISTER && p->op2==TK_COLLATE) ){
pColl = sqlite3GetCollSeq(pParse, ENC(db), 0, p->u.zToken);
break;
}
if( (op==TK_AGG_COLUMN || op==TK_COLUMN
|| op==TK_REGISTER || op==TK_TRIGGER)
&& p->pTab!=0
@@ -162,6 +154,14 @@ CollSeq *sqlite3ExprCollSeq(Parse *pParse, Expr *pExpr){
}
break;
}
if( op==TK_CAST || op==TK_UPLUS ){
p = p->pLeft;
continue;
}
if( op==TK_COLLATE || (op==TK_REGISTER && p->op2==TK_COLLATE) ){
pColl = sqlite3GetCollSeq(pParse, ENC(db), 0, p->u.zToken);
break;
}
if( p->flags & EP_Collate ){
if( p->pLeft && (p->pLeft->flags & EP_Collate)!=0 ){
p = p->pLeft;
@@ -1839,6 +1839,9 @@ static int exprNodeIsConstant(Walker *pWalker, Expr *pExpr){
testcase( pExpr->op==TK_COLUMN );
testcase( pExpr->op==TK_AGG_FUNCTION );
testcase( pExpr->op==TK_AGG_COLUMN );
if( ExprHasProperty(pExpr, EP_FixedCol) ){
return WRC_Continue;
}
if( pWalker->eCode==3 && pExpr->iTable==pWalker->u.iCur ){
return WRC_Continue;
}
@@ -1927,7 +1930,7 @@ static int exprNodeIsConstantOrGroupBy(Walker *pWalker, Expr *pExpr){
Expr *p = pGroupBy->a[i].pExpr;
if( sqlite3ExprCompare(0, pExpr, p, -1)<2 ){
CollSeq *pColl = sqlite3ExprNNCollSeq(pWalker->pParse, p);
if( sqlite3_stricmp("BINARY", pColl->zName)==0 ){
if( sqlite3IsBinary(pColl) ){
return WRC_Prune;
}
}
@@ -3581,6 +3584,9 @@ expr_code_doover:
}
case TK_COLUMN: {
int iTab = pExpr->iTable;
if( ExprHasProperty(pExpr, EP_FixedCol) ){
return sqlite3ExprCodeTarget(pParse, pExpr->pLeft,target);
}
if( iTab<0 ){
if( pParse->iSelfTab<0 ){
/* Generating CHECK constraints or inserting into partial index */
@@ -4942,7 +4948,8 @@ int sqlite3ExprCompare(Parse *pParse, Expr *pA, Expr *pB, int iTab){
if( (pA->flags & EP_Distinct)!=(pB->flags & EP_Distinct) ) return 2;
if( ALWAYS((combinedFlags & EP_TokenOnly)==0) ){
if( combinedFlags & EP_xIsSelect ) return 2;
if( sqlite3ExprCompare(pParse, pA->pLeft, pB->pLeft, iTab) ) return 2;
if( (combinedFlags & EP_FixedCol)==0
&& sqlite3ExprCompare(pParse, pA->pLeft, pB->pLeft, iTab) ) return 2;
if( sqlite3ExprCompare(pParse, pA->pRight, pB->pRight, iTab) ) return 2;
if( sqlite3ExprListCompare(pA->x.pList, pB->x.pList, iTab) ) return 2;
assert( (combinedFlags & EP_Reduced)==0 );

9
src/main.c
View File

@@ -910,6 +910,15 @@ static int binCollFunc(
return rc;
}
/*
** Return true if CollSeq is the default built-in BINARY.
*/
int sqlite3IsBinary(const CollSeq *p){
assert( p==0 || p->xCmp!=binCollFunc || p->pUser!=0
|| strcmp(p->zName,"BINARY")==0 );
return p==0 || (p->xCmp==binCollFunc && p->pUser==0);
}
/*
** Another built-in collating sequence: NOCASE.
**

180
src/select.c
View File

@@ -4074,7 +4074,168 @@ static int flattenSubquery(
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
/*
** A structure to keep track of all of the column values that fixed to
** a known value due to WHERE clause constraints of the form COLUMN=VALUE.
*/
typedef struct WhereConst WhereConst;
struct WhereConst {
Parse *pParse; /* Parsing context */
int nConst; /* Number for COLUMN=CONSTANT terms */
int nChng; /* Number of times a constant is propagated */
Expr **apExpr; /* [i*2] is COLUMN and [i*2+1] is VALUE */
};
/*
** Add a new entry to the pConst object
*/
static void constInsert(
WhereConst *pConst,
Expr *pColumn,
Expr *pValue
){
pConst->nConst++;
pConst->apExpr = sqlite3DbReallocOrFree(pConst->pParse->db, pConst->apExpr,
pConst->nConst*2*sizeof(Expr*));
if( pConst->apExpr==0 ){
pConst->nConst = 0;
}else{
if( ExprHasProperty(pValue, EP_FixedCol) ) pValue = pValue->pLeft;
pConst->apExpr[pConst->nConst*2-2] = pColumn;
pConst->apExpr[pConst->nConst*2-1] = pValue;
}
}
/*
** Find all terms of COLUMN=VALUE or VALUE=COLUMN in pExpr where VALUE
** is a constant expression and where the term must be true because it
** is part of the AND-connected terms of the expression. For each term
** found, add it to the pConst structure.
*/
static void findConstInWhere(WhereConst *pConst, Expr *pExpr){
Expr *pRight, *pLeft;
if( pExpr==0 ) return;
if( ExprHasProperty(pExpr, EP_FromJoin) ) return;
if( pExpr->op==TK_AND ){
findConstInWhere(pConst, pExpr->pRight);
findConstInWhere(pConst, pExpr->pLeft);
return;
}
if( pExpr->op!=TK_EQ ) return;
pRight = pExpr->pRight;
pLeft = pExpr->pLeft;
assert( pRight!=0 );
assert( pLeft!=0 );
if( pRight->op==TK_COLUMN
&& !ExprHasProperty(pRight, EP_FixedCol)
&& sqlite3ExprIsConstant(pLeft)
&& sqlite3IsBinary(sqlite3BinaryCompareCollSeq(pConst->pParse,pLeft,pRight))
){
constInsert(pConst, pRight, pLeft);
}else
if( pLeft->op==TK_COLUMN
&& !ExprHasProperty(pLeft, EP_FixedCol)
&& sqlite3ExprIsConstant(pRight)
&& sqlite3IsBinary(sqlite3BinaryCompareCollSeq(pConst->pParse,pLeft,pRight))
){
constInsert(pConst, pLeft, pRight);
}
}
/*
** This is a Walker expression callback. pExpr is a candidate expression
** to be replaced by a value. If pExpr is equivalent to one of the
** columns named in pWalker->u.pConst, then overwrite it with its
** corresponding value.
*/
static int propagateConstantExprRewrite(Walker *pWalker, Expr *pExpr){
int i;
WhereConst *pConst;
if( pExpr->op!=TK_COLUMN ) return WRC_Continue;
if( ExprHasProperty(pExpr, EP_FixedCol) ) return WRC_Continue;
pConst = pWalker->u.pConst;
for(i=0; i<pConst->nConst; i++){
Expr *pColumn = pConst->apExpr[i*2];
if( pColumn==pExpr ) continue;
if( pColumn->iTable!=pExpr->iTable ) continue;
if( pColumn->iColumn!=pExpr->iColumn ) continue;
/* A match is found. Add the EP_FixedCol property */
pConst->nChng++;
ExprClearProperty(pExpr, EP_Leaf);
ExprSetProperty(pExpr, EP_FixedCol);
assert( pExpr->pLeft==0 );
pExpr->pLeft = sqlite3ExprDup(pConst->pParse->db, pConst->apExpr[i*2+1], 0);
break;
}
return WRC_Prune;
}
/*
** The WHERE-clause constant propagation optimization.
**
** If the WHERE clause contains terms of the form COLUMN=CONSTANT or
** CONSTANT=COLUMN that must be tree (in other words, if the terms top-level
** AND-connected terms that are not part of a ON clause from a LEFT JOIN)
** then throughout the query replace all other occurrences of COLUMN
** with CONSTANT within the WHERE clause.
**
** For example, the query:
**
** SELECT * FROM t1, t2, t3 WHERE t1.a=39 AND t2.b=t1.a AND t3.c=t2.b
**
** Is transformed into
**
** SELECT * FROM t1, t2, t3 WHERE t1.a=39 AND t2.b=39 AND t3.c=39
**
** Return true if any transformations where made and false if not.
**
** Implementation note: Constant propagation is tricky due to affinity
** and collating sequence interactions. Consider this example:
**
** CREATE TABLE t1(a INT,b TEXT);
** INSERT INTO t1 VALUES(123,'0123');
** SELECT * FROM t1 WHERE a=123 AND b=a;
** SELECT * FROM t1 WHERE a=123 AND b=123;
**
** The two SELECT statements above should return different answers. b=a
** is alway true because the comparison uses numeric affinity, but b=123
** is false because it uses text affinity and '0123' is not the same as '123'.
** To work around this, the expression tree is not actually changed from
** "b=a" to "b=123" but rather the "a" in "b=a" is tagged with EP_FixedCol
** and the "123" value is hung off of the pLeft pointer. Code generator
** routines know to generate the constant "123" instead of looking up the
** column value. Also, to avoid collation problems, this optimization is
** only attempted if the "a=123" term uses the default BINARY collation.
*/
static int propagateConstants(
Parse *pParse, /* The parsing context */
Select *p /* The query in which to propagate constants */
){
WhereConst x;
Walker w;
int nChng = 0;
x.pParse = pParse;
do{
x.nConst = 0;
x.nChng = 0;
x.apExpr = 0;
findConstInWhere(&x, p->pWhere);
if( x.nConst ){
memset(&w, 0, sizeof(w));
w.pParse = pParse;
w.xExprCallback = propagateConstantExprRewrite;
w.xSelectCallback = sqlite3SelectWalkNoop;
w.xSelectCallback2 = 0;
w.walkerDepth = 0;
w.u.pConst = &x;
sqlite3WalkExpr(&w, p->pWhere);
sqlite3DbFree(x.pParse->db, x.apExpr);
nChng += x.nChng;
}
}while( x.nChng );
return nChng;
}
#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
@@ -5599,6 +5760,25 @@ int sqlite3Select(
}
#endif
/* Do the WHERE-clause constant propagation optimization if this is
** a join. No need to speed time on this operation for non-join queries
** as the equivalent optimization will be handled by query planner in
** sqlite3WhereBegin().
*/
if( pTabList->nSrc>1
&& OptimizationEnabled(db, SQLITE_PropagateConst)
&& propagateConstants(pParse, p)
){
#if SELECTTRACE_ENABLED
if( sqlite3SelectTrace & 0x100 ){
SELECTTRACE(0x100,pParse,p,("After constant propagation:\n"));
sqlite3TreeViewSelect(0, p, 0);
}
#endif
}else{
SELECTTRACE(0x100,pParse,p,("Constant propagation not helpful\n"));
}
/* For each term in the FROM clause, do two things:
** (1) Authorized unreferenced tables
** (2) Generate code for all sub-queries

5
src/sqliteInt.h
View File

@@ -1584,6 +1584,7 @@ struct sqlite3 {
#define SQLITE_PushDown 0x1000 /* The push-down optimization */
#define SQLITE_SimplifyJoin 0x2000 /* Convert LEFT JOIN to JOIN */
#define SQLITE_SkipScan 0x4000 /* Skip-scans */
#define SQLITE_PropagateConst 0x8000 /* The constant propagation opt */
#define SQLITE_AllOpts 0xffff /* All optimizations */
/*
@@ -2478,7 +2479,7 @@ struct Expr {
#define EP_FromJoin 0x000001 /* Originates in ON/USING clause of outer join */
#define EP_Agg 0x000002 /* Contains one or more aggregate functions */
#define EP_HasFunc 0x000004 /* Contains one or more functions of any kind */
/* 0x000008 // available for use */
#define EP_FixedCol 0x000008 /* TK_Column with a known fixed value */
#define EP_Distinct 0x000010 /* Aggregate function with DISTINCT keyword */
#define EP_VarSelect 0x000020 /* pSelect is correlated, not constant */
#define EP_DblQuoted 0x000040 /* token.z was originally in "..." */
@@ -3436,6 +3437,7 @@ struct Walker {
ExprList *pGroupBy; /* GROUP BY clause */
Select *pSelect; /* HAVING to WHERE clause ctx */
struct WindowRewrite *pRewrite; /* Window rewrite context */
struct WhereConst *pConst; /* WHERE clause constants */
} u;
};
@@ -4169,6 +4171,7 @@ int sqlite3MemdbInit(void);
const char *sqlite3ErrStr(int);
int sqlite3ReadSchema(Parse *pParse);
CollSeq *sqlite3FindCollSeq(sqlite3*,u8 enc, const char*,int);
int sqlite3IsBinary(const CollSeq*);
CollSeq *sqlite3LocateCollSeq(Parse *pParse, const char*zName);
CollSeq *sqlite3ExprCollSeq(Parse *pParse, Expr *pExpr);
CollSeq *sqlite3ExprNNCollSeq(Parse *pParse, Expr *pExpr);

3
src/treeview.c
View File

@@ -374,6 +374,9 @@ void sqlite3TreeViewExpr(TreeView *pView, const Expr *pExpr, u8 moreToFollow){
sqlite3TreeViewLine(pView, "{%d:%d}%s",
pExpr->iTable, pExpr->iColumn, zFlgs);
}
if( ExprHasProperty(pExpr, EP_FixedCol) ){
sqlite3TreeViewExpr(pView, pExpr->pLeft, 0);
}
break;
}
case TK_INTEGER: {

2
src/where.c
View File

@@ -3205,7 +3205,7 @@ const char *sqlite3_vtab_collation(sqlite3_index_info *pIdxInfo, int iCons){
if( pX->pLeft ){
pC = sqlite3BinaryCompareCollSeq(pHidden->pParse, pX->pLeft, pX->pRight);
}
zRet = (pC ? pC->zName : "BINARY");
zRet = (pC ? pC->zName : sqlite3StrBINARY);
}
return zRet;
}

2
src/wherecode.c
View File

@@ -883,7 +883,7 @@ static int codeCursorHintIsOrFunction(Walker *pWalker, Expr *pExpr){
static int codeCursorHintFixExpr(Walker *pWalker, Expr *pExpr){
int rc = WRC_Continue;
struct CCurHint *pHint = pWalker->u.pCCurHint;
if( pExpr->op==TK_COLUMN ){
if( pExpr->op==TK_COLUMN && !ExprHasProperty(pExpr, EP_FixedCol) ){
if( pExpr->iTable!=pHint->iTabCur ){
Vdbe *v = pWalker->pParse->pVdbe;
int reg = ++pWalker->pParse->nMem; /* Register for column value */

6
src/whereexpr.c
View File

@@ -859,7 +859,7 @@ static int termIsEquivalence(Parse *pParse, Expr *pExpr){
return 0;
}
pColl = sqlite3BinaryCompareCollSeq(pParse, pExpr->pLeft, pExpr->pRight);
if( pColl==0 || sqlite3StrICmp(pColl->zName, "BINARY")==0 ) return 1;
if( sqlite3IsBinary(pColl) ) return 1;
return sqlite3ExprCollSeqMatch(pParse, pExpr->pLeft, pExpr->pRight);
}
@@ -1200,7 +1200,7 @@ static void exprAnalyze(
}
*pC = c + 1;
}
zCollSeqName = noCase ? "NOCASE" : "BINARY";
zCollSeqName = noCase ? "NOCASE" : sqlite3StrBINARY;
pNewExpr1 = sqlite3ExprDup(db, pLeft, 0);
pNewExpr1 = sqlite3PExpr(pParse, TK_GE,
sqlite3ExprAddCollateString(pParse,pNewExpr1,zCollSeqName),
@@ -1450,7 +1450,7 @@ void sqlite3WhereClauseClear(WhereClause *pWC){
*/
Bitmask sqlite3WhereExprUsageNN(WhereMaskSet *pMaskSet, Expr *p){
Bitmask mask;
if( p->op==TK_COLUMN ){
if( p->op==TK_COLUMN && !ExprHasProperty(p, EP_FixedCol) ){
return sqlite3WhereGetMask(pMaskSet, p->iTable);
}else if( ExprHasProperty(p, EP_TokenOnly|EP_Leaf) ){
assert( p->op!=TK_IF_NULL_ROW );