Teach deparsing of CASE expressions to cope with the simplified forms

that simplify_boolean_equality() may leave behind.  This is only relevant
if the user writes something a bit silly, like CASE x=y WHEN TRUE THEN.
Per example from Michael Fuhr; may or may not explain bug #2106.

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index c7b8066cbfbaeb72c7d2f096f7467fea6654e926..5a102e5fed566d55f573bf7ae13d4e6d60951643 100644 (file)
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -3,7 +3,7 @@
  *             back to source text
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.209 2005/11/22 18:17:23 momjian Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.210 2005/12/10 19:21:03 tgl Exp $
  *
  *   This software is copyrighted by Jan Wieck - Hamburg.
  *
@@ -3389,6 +3389,7 @@ get_rule_expr(Node *node, deparse_context *context,
                foreach(temp, caseexpr->args)
                {
                    CaseWhen   *when = (CaseWhen *) lfirst(temp);
+                   Node       *w = (Node *) when->expr;
 
                    if (!PRETTY_INDENT(context))
                        appendStringInfoChar(buf, ' ');
@@ -3396,15 +3397,39 @@ get_rule_expr(Node *node, deparse_context *context,
                                         0, 0, 0);
                    if (caseexpr->arg)
                    {
-                       /* Show only the RHS of "CaseTestExpr = RHS" */
-                       Node       *rhs;
+                       /*
+                        * The parser should have produced WHEN clauses of
+                        * the form "CaseTestExpr = RHS"; we want to show
+                        * just the RHS.  If the user wrote something silly
+                        * like "CASE boolexpr WHEN TRUE THEN ...", then
+                        * the optimizer's simplify_boolean_equality() may
+                        * have reduced this to just "CaseTestExpr" or
+                        * "NOT CaseTestExpr", for which we have to show
+                        * "TRUE" or "FALSE".
+                        */
+                       if (IsA(w, OpExpr))
+                       {
+                           Node       *rhs;
 
-                       Assert(IsA(when->expr, OpExpr));
-                       rhs = (Node *) lsecond(((OpExpr *) when->expr)->args);
-                       get_rule_expr(rhs, context, false);
+                           Assert(IsA(linitial(((OpExpr *) w)->args),
+                                      CaseTestExpr));
+                           rhs = (Node *) lsecond(((OpExpr *) w)->args);
+                           get_rule_expr(rhs, context, false);
+                       }
+                       else if (IsA(w, CaseTestExpr))
+                           appendStringInfo(buf, "TRUE");
+                       else if (not_clause(w))
+                       {
+                           Assert(IsA(get_notclausearg((Expr *) w),
+                                      CaseTestExpr));
+                           appendStringInfo(buf, "FALSE");
+                       }
+                       else
+                           elog(ERROR, "unexpected CASE WHEN clause: %d",
+                                (int) nodeTag(w));
                    }
                    else
-                       get_rule_expr((Node *) when->expr, context, false);
+                       get_rule_expr(w, context, false);
                    appendStringInfo(buf, " THEN ");
                    get_rule_expr((Node *) when->result, context, true);
                }