Infer functional dependency past RelabelType

Vars hidden within a RelabelType would not be detected as compatible
with some functional dependency.  Repair by properly ignoring the
RelabelType.

Author: David Rowley
Reviewed-by: Tomas Vondra
Discussion: https://postgr.es/m/CAKJS1f-y-UEy=rsBXynBOgiW1fKMr_LVoYSGL9QOc36mLEC-ww@mail.gmail.com

diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c
index 2e7c0ad6ba61403eed83f8166711f7ac23556e86..9756fb83c0c855481be992b41b59fa0d8a806836 100644 (file)
--- a/src/backend/statistics/dependencies.c
+++ b/src/backend/statistics/dependencies.c
@@ -792,6 +792,14 @@ dependency_is_compatible_clause(Node *clause, Index relid, AttrNumber *attnum)
 
                var = (varonleft) ? linitial(expr->args) : lsecond(expr->args);
 
+               /*
+                * We may ignore any RelabelType node above the operand.  (There won't
+                * be more than one, since eval_const_expressions() has been applied
+                * already.)
+                */
+               if (IsA(var, RelabelType))
+                       var = (Var *) ((RelabelType *) var)->arg;
+
                /* We only support plain Vars for now */
                if (!IsA(var, Var))
                        return false;