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In the parse tree, combine LIMIT and OFFSET into a single expression rooted

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on a TK_LIMIT node, for a small code size reduction and performance increase,
and a reduction in code complexity.

FossilOrigin-Name: 3925facd942c9df663f9b29b1e6f94f6be14af8c2b99eb691bfc836b4c220826
This commit is contained in:
drh
2017-11-14 23:48:23 +00:00
parent 65efeaca83
commit 8c0833fb21
15 changed files with 92 additions and 140 deletions
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60
src/select.c
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@@ -74,7 +74,6 @@ static void clearSelect(sqlite3 *db, Select *p, int bFree){
sqlite3ExprDelete(db, p->pHaving);
sqlite3ExprListDelete(db, p->pOrderBy);
sqlite3ExprDelete(db, p->pLimit);
sqlite3ExprDelete(db, p->pOffset);
if( OK_IF_ALWAYS_TRUE(p->pWith) ) sqlite3WithDelete(db, p->pWith);
if( bFree ) sqlite3DbFreeNN(db, p);
p = pPrior;
@@ -107,8 +106,7 @@ Select *sqlite3SelectNew(
Expr *pHaving, /* the HAVING clause */
ExprList *pOrderBy, /* the ORDER BY clause */
u32 selFlags, /* Flag parameters, such as SF_Distinct */
Expr *pLimit, /* LIMIT value. NULL means not used */
Expr *pOffset /* OFFSET value. NULL means no offset */
Expr *pLimit /* LIMIT value. NULL means not used */
){
Select *pNew;
Select standin;
@@ -141,10 +139,7 @@ Select *sqlite3SelectNew(
pNew->pPrior = 0;
pNew->pNext = 0;
pNew->pLimit = pLimit;
pNew->pOffset = pOffset;
pNew->pWith = 0;
assert( pOffset==0 || pLimit!=0 || pParse->nErr>0
|| pParse->db->mallocFailed!=0 );
if( pParse->db->mallocFailed ) {
clearSelect(pParse->db, pNew, pNew!=&standin);
pNew = 0;
@@ -1874,7 +1869,7 @@ Vdbe *sqlite3GetVdbe(Parse *pParse){
/*
** Compute the iLimit and iOffset fields of the SELECT based on the
** pLimit and pOffset expressions. pLimit and pOffset hold the expressions
** pLimit expressions. pLimit->pLeft and pLimit->pRight hold the expressions
** that appear in the original SQL statement after the LIMIT and OFFSET
** keywords. Or NULL if those keywords are omitted. iLimit and iOffset
** are the integer memory register numbers for counters used to compute
@@ -1882,15 +1877,15 @@ Vdbe *sqlite3GetVdbe(Parse *pParse){
** iLimit and iOffset are negative.
**
** This routine changes the values of iLimit and iOffset only if
** a limit or offset is defined by pLimit and pOffset. iLimit and
** iOffset should have been preset to appropriate default values (zero)
** a limit or offset is defined by pLimit->pLeft and pLimit->pRight. iLimit
** and iOffset should have been preset to appropriate default values (zero)
** prior to calling this routine.
**
** The iOffset register (if it exists) is initialized to the value
** of the OFFSET. The iLimit register is initialized to LIMIT. Register
** iOffset+1 is initialized to LIMIT+OFFSET.
**
** Only if pLimit!=0 or pOffset!=0 do the limit registers get
** Only if pLimit->pLeft!=0 do the limit registers get
** redefined. The UNION ALL operator uses this property to force
** the reuse of the same limit and offset registers across multiple
** SELECT statements.
@@ -1900,6 +1895,8 @@ static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
int iLimit = 0;
int iOffset;
int n;
Expr *pLimit = p->pLimit;
if( p->iLimit ) return;
/*
@@ -1909,12 +1906,13 @@ static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
** no rows.
*/
sqlite3ExprCacheClear(pParse);
assert( p->pOffset==0 || p->pLimit!=0 );
if( p->pLimit ){
if( pLimit ){
assert( pLimit->op==TK_LIMIT );
assert( pLimit->pLeft!=0 );
p->iLimit = iLimit = ++pParse->nMem;
v = sqlite3GetVdbe(pParse);
assert( v!=0 );
if( sqlite3ExprIsInteger(p->pLimit, &n) ){
if( sqlite3ExprIsInteger(pLimit->pLeft, &n) ){
sqlite3VdbeAddOp2(v, OP_Integer, n, iLimit);
VdbeComment((v, "LIMIT counter"));
if( n==0 ){
@@ -1924,15 +1922,15 @@ static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
p->selFlags |= SF_FixedLimit;
}
}else{
sqlite3ExprCode(pParse, p->pLimit, iLimit);
sqlite3ExprCode(pParse, pLimit->pLeft, iLimit);
sqlite3VdbeAddOp1(v, OP_MustBeInt, iLimit); VdbeCoverage(v);
VdbeComment((v, "LIMIT counter"));
sqlite3VdbeAddOp2(v, OP_IfNot, iLimit, iBreak); VdbeCoverage(v);
}
if( p->pOffset ){
if( pLimit->pRight ){
p->iOffset = iOffset = ++pParse->nMem;
pParse->nMem++; /* Allocate an extra register for limit+offset */
sqlite3ExprCode(pParse, p->pOffset, iOffset);
sqlite3ExprCode(pParse, pLimit->pRight, iOffset);
sqlite3VdbeAddOp1(v, OP_MustBeInt, iOffset); VdbeCoverage(v);
VdbeComment((v, "OFFSET counter"));
sqlite3VdbeAddOp3(v, OP_OffsetLimit, iLimit, iOffset+1, iOffset);
@@ -2062,7 +2060,7 @@ static void generateWithRecursiveQuery(
int i; /* Loop counter */
int rc; /* Result code */
ExprList *pOrderBy; /* The ORDER BY clause */
Expr *pLimit, *pOffset; /* Saved LIMIT and OFFSET */
Expr *pLimit; /* Saved LIMIT and OFFSET */
int regLimit, regOffset; /* Registers used by LIMIT and OFFSET */
/* Obtain authorization to do a recursive query */
@@ -2073,10 +2071,9 @@ static void generateWithRecursiveQuery(
p->nSelectRow = 320; /* 4 billion rows */
computeLimitRegisters(pParse, p, addrBreak);
pLimit = p->pLimit;
pOffset = p->pOffset;
regLimit = p->iLimit;
regOffset = p->iOffset;
p->pLimit = p->pOffset = 0;
p->pLimit = 0;
p->iLimit = p->iOffset = 0;
pOrderBy = p->pOrderBy;
@@ -2169,7 +2166,6 @@ end_of_recursive_query:
sqlite3ExprListDelete(pParse->db, p->pOrderBy);
p->pOrderBy = pOrderBy;
p->pLimit = pLimit;
p->pOffset = pOffset;
return;
}
#endif /* SQLITE_OMIT_CTE */
@@ -2205,7 +2201,6 @@ static int multiSelectValues(
assert( p->selFlags & SF_Values );
assert( p->op==TK_ALL || (p->op==TK_SELECT && p->pPrior==0) );
assert( p->pLimit==0 );
assert( p->pOffset==0 );
assert( p->pNext==0 || p->pEList->nExpr==p->pNext->pEList->nExpr );
if( p->pPrior==0 ) break;
assert( p->pPrior->pNext==p );
@@ -2332,11 +2327,9 @@ static int multiSelect(
pPrior->iLimit = p->iLimit;
pPrior->iOffset = p->iOffset;
pPrior->pLimit = p->pLimit;
pPrior->pOffset = p->pOffset;
explainSetInteger(iSub1, pParse->iNextSelectId);
rc = sqlite3Select(pParse, pPrior, &dest);
p->pLimit = 0;
p->pOffset = 0;
if( rc ){
goto multi_select_end;
}
@@ -2358,7 +2351,7 @@ static int multiSelect(
p->pPrior = pPrior;
p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
if( pPrior->pLimit
&& sqlite3ExprIsInteger(pPrior->pLimit, &nLimit)
&& sqlite3ExprIsInteger(pPrior->pLimit->pLeft, &nLimit)
&& nLimit>0 && p->nSelectRow > sqlite3LogEst((u64)nLimit)
){
p->nSelectRow = sqlite3LogEst((u64)nLimit);
@@ -2373,7 +2366,7 @@ static int multiSelect(
int unionTab; /* Cursor number of the temporary table holding result */
u8 op = 0; /* One of the SRT_ operations to apply to self */
int priorOp; /* The SRT_ operation to apply to prior selects */
Expr *pLimit, *pOffset; /* Saved values of p->nLimit and p->nOffset */
Expr *pLimit; /* Saved values of p->nLimit */
int addr;
SelectDest uniondest;
@@ -2385,7 +2378,6 @@ static int multiSelect(
** right.
*/
assert( p->pLimit==0 ); /* Not allowed on leftward elements */
assert( p->pOffset==0 ); /* Not allowed on leftward elements */
unionTab = dest.iSDParm;
}else{
/* We will need to create our own temporary table to hold the
@@ -2421,8 +2413,6 @@ static int multiSelect(
p->pPrior = 0;
pLimit = p->pLimit;
p->pLimit = 0;
pOffset = p->pOffset;
p->pOffset = 0;
uniondest.eDest = op;
explainSetInteger(iSub2, pParse->iNextSelectId);
rc = sqlite3Select(pParse, p, &uniondest);
@@ -2438,7 +2428,6 @@ static int multiSelect(
}
sqlite3ExprDelete(db, p->pLimit);
p->pLimit = pLimit;
p->pOffset = pOffset;
p->iLimit = 0;
p->iOffset = 0;
@@ -2466,7 +2455,7 @@ static int multiSelect(
default: assert( p->op==TK_INTERSECT ); {
int tab1, tab2;
int iCont, iBreak, iStart;
Expr *pLimit, *pOffset;
Expr *pLimit;
int addr;
SelectDest intersectdest;
int r1;
@@ -2502,8 +2491,6 @@ static int multiSelect(
p->pPrior = 0;
pLimit = p->pLimit;
p->pLimit = 0;
pOffset = p->pOffset;
p->pOffset = 0;
intersectdest.iSDParm = tab2;
explainSetInteger(iSub2, pParse->iNextSelectId);
rc = sqlite3Select(pParse, p, &intersectdest);
@@ -2513,7 +2500,6 @@ static int multiSelect(
if( p->nSelectRow>pPrior->nSelectRow ) p->nSelectRow = pPrior->nSelectRow;
sqlite3ExprDelete(db, p->pLimit);
p->pLimit = pLimit;
p->pOffset = pOffset;
/* Generate code to take the intersection of the two temporary
** tables.
@@ -2992,8 +2978,6 @@ static int multiSelectOrderBy(
}
sqlite3ExprDelete(db, p->pLimit);
p->pLimit = 0;
sqlite3ExprDelete(db, p->pOffset);
p->pOffset = 0;
regAddrA = ++pParse->nMem;
regAddrB = ++pParse->nMem;
@@ -3457,7 +3441,7 @@ static int flattenSubquery(
** became arbitrary expressions, we were forced to add restrictions (13)
** and (14). */
if( pSub->pLimit && p->pLimit ) return 0; /* Restriction (13) */
if( pSub->pOffset ) return 0; /* Restriction (14) */
if( pSub->pLimit && pSub->pLimit->pRight ) return 0; /* Restriction (14) */
if( (p->selFlags & SF_Compound)!=0 && pSub->pLimit ){
return 0; /* Restriction (15) */
}
@@ -3605,16 +3589,13 @@ static int flattenSubquery(
Select *pNew;
ExprList *pOrderBy = p->pOrderBy;
Expr *pLimit = p->pLimit;
Expr *pOffset = p->pOffset;
Select *pPrior = p->pPrior;
p->pOrderBy = 0;
p->pSrc = 0;
p->pPrior = 0;
p->pLimit = 0;
p->pOffset = 0;
pNew = sqlite3SelectDup(db, p, 0);
sqlite3SelectSetName(pNew, pSub->zSelName);
p->pOffset = pOffset;
p->pLimit = pLimit;
p->pOrderBy = pOrderBy;
p->pSrc = pSrc;
@@ -4080,7 +4061,6 @@ static int convertCompoundSelectToSubquery(Walker *pWalker, Select *p){
assert( pNew->pPrior!=0 );
pNew->pPrior->pNext = pNew;
pNew->pLimit = 0;
pNew->pOffset = 0;
return WRC_Continue;
}