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Scan the table backwards if there is an ORDER BY ... DESC clause that can

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be satisfied by an index. (CVS 795)

FossilOrigin-Name: c7a3487981de0ed5b43ea3ff4d46ab4437068dca
This commit is contained in:
drh
2002-12-04 20:01:06 +00:00
parent 2dcc9aa2a8
commit c045ec51be
5 changed files with 135 additions and 47 deletions
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52
src/vdbe.c
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@@ -36,7 +36,7 @@
** in this file for details. If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.185 2002/12/02 04:25:21 drh Exp $
** $Id: vdbe.c,v 1.186 2002/12/04 20:01:06 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>
@@ -3354,8 +3354,19 @@ case OP_Close: {
** If there are no records greater than the key and P2 is not zero,
** then an immediate jump to P2 is made.
**
** See also: Found, NotFound, Distinct
** See also: Found, NotFound, Distinct, MoveLt
*/
/* Opcode: MoveLt P1 P2 *
**
** Pop the top of the stack and use its value as a key. Reposition
** cursor P1 so that it points to the entry with the largest key that is
** less than the key popped from the stack.
** If there are no records less than than the key and P2
** is not zero then an immediate jump to P2 is made.
**
** See also: MoveTo
*/
case OP_MoveLt:
case OP_MoveTo: {
int i = pOp->p1;
int tos = p->tos;
@@ -3363,7 +3374,7 @@ case OP_MoveTo: {
VERIFY( if( tos<0 ) goto not_enough_stack; )
if( i>=0 && i<p->nCursor && (pC = &p->aCsr[i])->pCursor!=0 ){
int res;
int res, oc;
if( aStack[tos].flags & STK_Int ){
int iKey = intToKey(aStack[tos].i);
sqliteBtreeMoveto(pC->pCursor, (char*)&iKey, sizeof(int), &res);
@@ -3376,12 +3387,19 @@ case OP_MoveTo: {
}
pC->nullRow = 0;
sqlite_search_count++;
if( res<0 ){
oc = pOp->opcode;
if( oc==OP_MoveTo && res<0 ){
sqliteBtreeNext(pC->pCursor, &res);
pC->recnoIsValid = 0;
if( res && pOp->p2>0 ){
pc = pOp->p2 - 1;
}
}else if( oc==OP_MoveLt && res>=0 ){
sqliteBtreePrevious(pC->pCursor, &res);
pC->recnoIsValid = 0;
if( res && pOp->p2>0 ){
pc = pOp->p2 - 1;
}
}
}
POPSTACK;
@@ -4026,7 +4044,17 @@ case OP_Rewind: {
** table or index. If there are no more key/value pairs then fall through
** to the following instruction. But if the cursor advance was successful,
** jump immediately to P2.
**
** See also: Prev
*/
/* Opcode: Prev P1 P2 *
**
** Back up cursor P1 so that it points to the previous key/data pair in its
** table or index. If there is no previous key/value pairs then fall through
** to the following instruction. But if the cursor backup was successful,
** jump immediately to P2.
*/
case OP_Prev:
case OP_Next: {
int i = pOp->p1;
BtCursor *pCrsr;
@@ -4036,7 +4064,8 @@ case OP_Next: {
if( p->aCsr[i].nullRow ){
res = 1;
}else{
rc = sqliteBtreeNext(pCrsr, &res);
rc = pOp->opcode==OP_Next ? sqliteBtreeNext(pCrsr, &res) :
sqliteBtreePrevious(pCrsr, &res);
p->aCsr[i].nullRow = res;
}
if( res==0 ){
@@ -4164,6 +4193,15 @@ case OP_IdxRecno: {
** then jump to P2. Otherwise fall through to the next instruction.
** In either case, the stack is popped once.
*/
/* Opcode: IdxLT P1 P2 *
**
** Compare the top of the stack against the key on the index entry that
** cursor P1 is currently pointing to. Ignore the last 4 bytes of the
** index entry. If the index entry is less than the top of the stack
** then jump to P2. Otherwise fall through to the next instruction.
** In either case, the stack is popped once.
*/
case OP_IdxLT:
case OP_IdxGT:
case OP_IdxGE: {
int i= pOp->p1;
@@ -4178,7 +4216,9 @@ case OP_IdxGE: {
if( rc!=SQLITE_OK ){
break;
}
if( pOp->opcode==OP_IdxGE ){
if( pOp->opcode==OP_IdxLT ){
res = -res;
}else if( pOp->opcode==OP_IdxGE ){
res++;
}
if( res>0 ){