diff options
Diffstat (limited to 'src/backend/utils/adt/selfuncs.c')
| -rw-r--r-- | src/backend/utils/adt/selfuncs.c | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 0fcfdcbf322..56248a93b6a 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -15,7 +15,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.214.2.5 2007/05/05 17:05:55 mha Exp $ + * $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.214.2.6 2007/08/31 23:35:29 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -1386,11 +1386,24 @@ booltestsel(PlannerInfo *root, BoolTestType booltesttype, Node *arg, */ Selectivity nulltestsel(PlannerInfo *root, NullTestType nulltesttype, - Node *arg, int varRelid) + Node *arg, int varRelid, JoinType jointype) { VariableStatData vardata; double selec; + /* + * Special hack: an IS NULL test being applied at an outer join should not + * be taken at face value, since it's very likely being used to select the + * outer-side rows that don't have a match, and thus its selectivity has + * nothing whatever to do with the statistics of the original table + * column. We do not have nearly enough context here to determine its + * true selectivity, so for the moment punt and guess at 0.5. Eventually + * the planner should be made to provide enough info about the clause's + * context to let us do better. + */ + if (IS_OUTER_JOIN(jointype) && nulltesttype == IS_NULL) + return (Selectivity) 0.5; + examine_variable(root, arg, varRelid, &vardata); if (HeapTupleIsValid(vardata.statsTuple)) |