diff options
Diffstat (limited to 'src/backend/optimizer/prep/prepjointree.c')
| -rw-r--r-- | src/backend/optimizer/prep/prepjointree.c | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c index 74829a09d1c..2e0d41a8d1f 100644 --- a/src/backend/optimizer/prep/prepjointree.c +++ b/src/backend/optimizer/prep/prepjointree.c @@ -2611,6 +2611,17 @@ pullup_replace_vars_callback(Var *var, * the plan in cases where the nullingrels get removed again * later by outer join reduction. * + * Note that we don't force wrapping of expressions containing + * lateral references, so long as they also contain Vars/PHVs + * of the subquery. This is okay because of the restriction + * to strict constructs: if the subquery's Vars/PHVs have been + * forced to NULL by an outer join then the end result of the + * expression will be NULL too, regardless of the lateral + * references. So it's not necessary to force the expression + * to be evaluated below the outer join. This can be a very + * valuable optimization, because it may allow us to avoid + * using a nested loop to pass the lateral reference down. + * * This analysis could be tighter: in particular, a non-strict * construct hidden within a lower-level PlaceHolderVar is not * reason to add another PHV. But for now it doesn't seem @@ -2675,9 +2686,13 @@ pullup_replace_vars_callback(Var *var, } else { - /* There should be lower-level Vars/PHVs we can modify */ + /* + * There should be Vars/PHVs within the expression that we can + * modify. Per above discussion, modify only Vars/PHVs of the + * subquery, not lateral references. + */ newnode = add_nulling_relids(newnode, - NULL, /* modify all Vars/PHVs */ + rcon->relids, var->varnullingrels); /* Assert we did put the varnullingrels into the expression */ Assert(bms_is_subset(var->varnullingrels, |