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An optimization: avoid the use of an intermediate table on UNION ALL if there

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is no ORDER BY clause. (CVS 637)

FossilOrigin-Name: 8aa73ce61268a50d353d9a5c878461290195525f
This commit is contained in:
drh
2002-06-22 02:33:38 +00:00
parent d11d382c99
commit f46f905a1e
6 changed files with 64 additions and 31 deletions
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50
src/select.c
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@@ -12,7 +12,7 @@
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.96 2002/06/21 23:01:50 drh Exp $
** $Id: select.c,v 1.97 2002/06/22 02:33:38 drh Exp $
*/
#include "sqliteInt.h"
@@ -441,26 +441,28 @@ static int selectInnerLoop(
break;
}
/* Send the data to the callback function.
*/
case SRT_Callback:
case SRT_Sorter: {
if( pOrderBy ){
sqliteVdbeAddOp(v, OP_SortMakeRec, nColumn, 0);
pushOntoSorter(pParse, v, pOrderBy);
}else{
assert( eDest==SRT_Callback );
sqliteVdbeAddOp(v, OP_Callback, nColumn, 0);
}
break;
}
/* Discard the results. This is used for SELECT statements inside
** the body of a TRIGGER. The purpose of such selects is to call
** user-defined functions that have side effects. We do not care
** about the actual results of the select.
*/
case SRT_Discard: {
sqliteVdbeAddOp(v, OP_Pop, nColumn, 0);
break;
}
/* Send the data to the callback function.
*/
default: {
assert( eDest==SRT_Callback );
if( pOrderBy ){
sqliteVdbeAddOp(v, OP_SortMakeRec, nColumn, 0);
pushOntoSorter(pParse, v, pOrderBy);
}else{
sqliteVdbeAddOp(v, OP_Callback, nColumn, 0);
}
assert( eDest==SRT_Discard );
sqliteVdbeAddOp(v, OP_Pop, nColumn, 0);
break;
}
}
@@ -482,6 +484,7 @@ static void generateSortTail(
){
int end = sqliteVdbeMakeLabel(v);
int addr;
if( eDest==SRT_Sorter ) return;
sqliteVdbeAddOp(v, OP_Sort, 0, 0);
addr = sqliteVdbeAddOp(v, OP_SortNext, 0, end);
if( p->nOffset>0 ){
@@ -518,7 +521,7 @@ static void generateSortTail(
break;
}
default: {
assert( end==0 ); /* Cannot happen */
/* Do nothing */
break;
}
}
@@ -998,11 +1001,22 @@ static int multiSelect(Parse *pParse, Select *p, int eDest, int iParm){
eDest = SRT_Table;
}
/* Process the UNION or INTERSECTION
/* Generate code for the left and right SELECT statements.
*/
base = pParse->nTab;
switch( p->op ){
case TK_ALL:
case TK_ALL: {
if( p->pOrderBy==0 ){
rc = sqliteSelect(pParse, pPrior, eDest, iParm, 0, 0, 0);
if( rc ) return rc;
p->pPrior = 0;
rc = sqliteSelect(pParse, p, eDest, iParm, 0, 0, 0);
p->pPrior = pPrior;
if( rc ) return rc;
break;
}
/* For UNION ALL ... ORDER BY fall through to the next case */
}
case TK_EXCEPT:
case TK_UNION: {
int unionTab; /* Cursor number of the temporary table holding result */