Don't let transform_null_equals=on affect CASE foo WHEN NULL ... constructs.

transform_null_equals is only supposed to affect "foo = NULL" expressions
given directly by the user, not the internal "foo = NULL" expression
generated from CASE-WHEN.

This fixes bug #6242, reported by Sergey. Backpatch to all supported
branches.

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 65d03adc4942e16ecbf0dd057eaa5f90a534a4e1..79328c997974ad5c50a016b7ade3c3eb4d64156e 100644 (file)
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -836,12 +836,15 @@ transformAExprOp(ParseState *pstate, A_Expr *a)
        /*
         * Special-case "foo = NULL" and "NULL = foo" for compatibility with
         * standards-broken products (like Microsoft's).  Turn these into IS NULL
-        * exprs.
+        * exprs. (If either side is a CaseTestExpr, then the expression was
+        * generated internally from a CASE-WHEN expression, and
+        * transform_null_equals does not apply.)
         */
        if (Transform_null_equals &&
                list_length(a->name) == 1 &&
                strcmp(strVal(linitial(a->name)), "=") == 0 &&
-               (exprIsNullConstant(lexpr) || exprIsNullConstant(rexpr)))
+               (exprIsNullConstant(lexpr) || exprIsNullConstant(rexpr)) &&
+               (!IsA(lexpr, CaseTestExpr) && !IsA(rexpr, CaseTestExpr)))
        {
                NullTest   *n = makeNode(NullTest);