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Overview
| Comment: | An experimental optimization to DISTINCT that causes an immediate exit of the inner loop of a join following each output row if the inner loop does not contribute any columns to the result set. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | distinct-early-out |
| Files: | files | file ages | folders |
| SHA3-256: |
a33f88acd7e02361fac1874c71dae1db |
| User & Date: | drh 2017-11-21 23:47:42 |
Context
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2017-11-21
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| 23:47 | An experimental optimization to DISTINCT that causes an immediate exit of the inner loop of a join following each output row if the inner loop does not contribute any columns to the result set. Leaf check-in: a33f88ac user: drh tags: distinct-early-out | |
| 23:38 | Fix the skip-ahead-distinct optimization on joins for cases there the table in the inner loop of the join does not contribute any columns to the result set. Proposed fix for ticket [ef9318757b152e3a2] check-in: 2dcef5a9 user: drh tags: trunk | |
Changes
Changes to src/where.c.
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Parse *pParse = pWInfo->pParse;
Vdbe *v = pParse->pVdbe;
int i;
WhereLevel *pLevel;
WhereLoop *pLoop;
SrcList *pTabList = pWInfo->pTabList;
sqlite3 *db = pParse->db;
/* Generate loop termination code.
*/
VdbeModuleComment((v, "End WHERE-core"));
sqlite3ExprCacheClear(pParse);
for(i=pWInfo->nLevel-1; i>=0; i--){
int addr;
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Parse *pParse = pWInfo->pParse; Vdbe *v = pParse->pVdbe; int i; WhereLevel *pLevel; WhereLoop *pLoop; SrcList *pTabList = pWInfo->pTabList; sqlite3 *db = pParse->db; /* For a DISTINCT join in which no columns of inner loops appear in ** the result set, put a jump right after the inner loop body that ** causes the unused inner loops to exit. */ if( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED && pWInfo->nLevel>1 ){ Bitmask tabUsed; tabUsed = sqlite3WhereExprListUsage(&pWInfo->sMaskSet, pWInfo->pResultSet); for(i=pWInfo->nLevel-1; i>=0; i--){ pLoop = pWInfo->a[i].pWLoop; if( (tabUsed & pLoop->maskSelf)!=0 ) break; } if( i<pWInfo->nLevel-1 ){ sqlite3VdbeGoto(v, pWInfo->a[i].addrCont); } } /* Generate loop termination code. */ VdbeModuleComment((v, "End WHERE-core")); sqlite3ExprCacheClear(pParse); for(i=pWInfo->nLevel-1; i>=0; i--){ int addr; |