diff options
Diffstat (limited to 'src/where.c')
| -rw-r--r-- | src/where.c | 17 |
1 files changed, 10 insertions, 7 deletions
diff --git a/src/where.c b/src/where.c index 5a3d44f9e..95bbdb157 100644 --- a/src/where.c +++ b/src/where.c @@ -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 */ } |