diff options
Diffstat (limited to 'src/backend/optimizer/util/tlist.c')
| -rw-r--r-- | src/backend/optimizer/util/tlist.c | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/src/backend/optimizer/util/tlist.c b/src/backend/optimizer/util/tlist.c index 9728ac8333b..5dc4b835fa3 100644 --- a/src/backend/optimizer/util/tlist.c +++ b/src/backend/optimizer/util/tlist.c @@ -159,6 +159,43 @@ get_tlist_exprs(List *tlist, bool includeJunk) /* + * tlist_same_exprs + * Check whether two target lists contain the same expressions + * + * Note: this function is used to decide whether it's safe to jam a new tlist + * into a non-projection-capable plan node. Obviously we can't do that unless + * the node's tlist shows it already returns the column values we want. + * However, we can ignore the TargetEntry attributes resname, ressortgroupref, + * resorigtbl, resorigcol, and resjunk, because those are only labelings that + * don't affect the row values computed by the node. (Moreover, if we didn't + * ignore them, we'd frequently fail to make the desired optimization, since + * the planner tends to not bother to make resname etc. valid in intermediate + * plan nodes.) Note that on success, the caller must still jam the desired + * tlist into the plan node, else it won't have the desired labeling fields. + */ +bool +tlist_same_exprs(List *tlist1, List *tlist2) +{ + ListCell *lc1, + *lc2; + + if (list_length(tlist1) != list_length(tlist2)) + return false; /* not same length, so can't match */ + + forboth(lc1, tlist1, lc2, tlist2) + { + TargetEntry *tle1 = (TargetEntry *) lfirst(lc1); + TargetEntry *tle2 = (TargetEntry *) lfirst(lc2); + + if (!equal(tle1->expr, tle2->expr)) + return false; + } + + return true; +} + + +/* * Does tlist have same output datatypes as listed in colTypes? * * Resjunk columns are ignored if junkOK is true; otherwise presence of |