database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-14 00:22:38 +03:00
Code Activity

In the query planner, do not consider index X to be a proper subset of

Browse Source 
index Y if X is a covering index but Y is not.

FossilOrigin-Name: ee31c04353cd75ea4bbadee2994c30d3808b696a4f680187502d104902988a5d
This commit is contained in:
drh
2017-10-15 22:16:25 +00:00
parent 835cd436e1
commit 47b1d68f25
4 changed files with 23 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
src/where.c
View File

@@ -1885,16 +1885,15 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
** Return TRUE if all of the following are true:
**
** (1) X has the same or lower cost that Y
** (2) X is a proper subset of Y
** (3) X skips at least as many columns as Y
**
** By "proper subset" we mean that X uses fewer WHERE clause terms
** than Y and that every WHERE clause term used by X is also used
** by 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. The third rule
** 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.
*/
@@ -1918,6 +1917,10 @@ static int whereLoopCheaperProperSubset(
}
if( j<0 ) return 0; /* X not a subset of Y since term X[i] not used by Y */
}
if( (pX->wsFlags&WHERE_IDX_ONLY)!=0
&& (pY->wsFlags&WHERE_IDX_ONLY)==0 ){
return 0; /* Constraint (5) */
}
return 1; /* All conditions meet */
}