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Overview
| Comment: | Improved comments, including a typo fix, on the whereLoopCheaperProperSubset() function. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
700a3c694438ca6cca185d0097f24799 |
| User & Date: | drh 2017-10-16 11:50:12 |
Context
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2017-10-17
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| 13:44 | Fix the ".check" command of the command-line shell to return 1 (error) rather than 2 (exit) on a test failure. check-in: e2af0cc6 user: drh tags: trunk | |
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2017-10-16
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| 11:50 | Improved comments, including a typo fix, on the whereLoopCheaperProperSubset() function. check-in: 700a3c69 user: drh tags: trunk | |
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2017-10-15
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| 22:16 | In the query planner, do not consider index X to be a proper subset of index Y if X is a covering index but Y is not. check-in: ee31c043 user: drh tags: trunk | |
Changes
Changes to src/where.c.
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}
}
/*
** Return TRUE if all of the following are true:
**
** (1) X has the same or lower cost that Y
** (2) X users fewer WHERE clause terms than Y
** (3) Every WHERE clause term used by X is also used by Y
** (4) X skips at least as many columns as Y
** (5) If X is a covering index, than Y is too
**
** Conditions (2) and (3) mean that X is a "proper subset" of Y.
** If X is a proper subset of Y then Y is a better choice and ought
** to have a lower cost. This routine returns TRUE when that cost
** relationship is inverted and needs to be adjusted. Constraint (4)
** was added because if X uses skip-scan less than Y it still might
** deserve a lower cost even if it is a proper subset of Y.
*/
static int whereLoopCheaperProperSubset(
const WhereLoop *pX, /* First WhereLoop to compare */
const WhereLoop *pY /* Compare against this WhereLoop */
){
int i, j;
if( pX->nLTerm-pX->nSkip >= pY->nLTerm-pY->nSkip ){
|
| | > > |
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} } /* ** Return TRUE if all of the following are true: ** ** (1) X has the same or lower cost that Y ** (2) X uses fewer WHERE clause terms than Y ** (3) Every WHERE clause term used by X is also used by Y ** (4) X skips at least as many columns as Y ** (5) If X is a covering index, than Y is too ** ** Conditions (2) and (3) mean that X is a "proper subset" of Y. ** If X is a proper subset of Y then Y is a better choice and ought ** to have a lower cost. This routine returns TRUE when that cost ** relationship is inverted and needs to be adjusted. Constraint (4) ** was added because if X uses skip-scan less than Y it still might ** deserve a lower cost even if it is a proper subset of Y. Constraint (5) ** was added because a covering index probably deserves to have a lower cost ** than a non-covering index even if it is a proper subset. */ static int whereLoopCheaperProperSubset( const WhereLoop *pX, /* First WhereLoop to compare */ const WhereLoop *pY /* Compare against this WhereLoop */ ){ int i, j; if( pX->nLTerm-pX->nSkip >= pY->nLTerm-pY->nSkip ){ |