Reimplement CASE val WHEN compval1 THEN ... WHEN compval2 THEN ... END

so that the 'val' is computed only once, per recent discussion.  The
speedup is not much when 'val' is just a simple variable, but could be
significant for larger expressions.  More importantly this avoids issues
with multiple evaluations of a volatile 'val', and it allows the CASE
expression to be reverse-listed in its original form by ruleutils.c.

1 files changed, 19 insertions, 4 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 7e1513796db..3960152f387 100644
--- 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 1.162 2004/01/31 05:09:40 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.163 2004/03/17 20:48:42 tgl Exp $
  *
  *	  This software is copyrighted by Jan Wieck - Hamburg.
  *
@@ -2564,7 +2564,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_ArrayExpr:		/* other separators */
 				case T_CoalesceExpr:	/* own parentheses */
 				case T_NullIfExpr:		/* other separators */
-				case T_Aggref:	/* own parentheses */
+				case T_Aggref:			/* own parentheses */
 				case T_CaseExpr:		/* other separators */
 					return true;
 				default:
@@ -2610,7 +2610,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_ArrayExpr:		/* other separators */
 				case T_CoalesceExpr:	/* own parentheses */
 				case T_NullIfExpr:		/* other separators */
-				case T_Aggref:	/* own parentheses */
+				case T_Aggref:			/* own parentheses */
 				case T_CaseExpr:		/* other separators */
 					return true;
 				default:
@@ -3026,6 +3026,11 @@ get_rule_expr(Node *node, deparse_context *context,
 
 				appendContextKeyword(context, "CASE",
 									 0, PRETTYINDENT_VAR, 0);
+				if (caseexpr->arg)
+				{
+					appendStringInfoChar(buf, ' ');
+					get_rule_expr((Node *) caseexpr->arg, context, true);
+				}
 				foreach(temp, caseexpr->args)
 				{
 					CaseWhen   *when = (CaseWhen *) lfirst(temp);
@@ -3034,7 +3039,17 @@ get_rule_expr(Node *node, deparse_context *context,
 						appendStringInfoChar(buf, ' ');
 					appendContextKeyword(context, "WHEN ",
 										 0, 0, 0);
-					get_rule_expr((Node *) when->expr, context, false);
+					if (caseexpr->arg)
+					{
+						/* Show only the RHS of "CaseTestExpr = RHS" */
+						Node   *rhs;
+
+						Assert(IsA(when->expr, OpExpr));
+						rhs = (Node *) lsecond(((OpExpr *) when->expr)->args);
+						get_rule_expr(rhs, context, false);
+					}
+					else
+						get_rule_expr((Node *) when->expr, context, false);
 					appendStringInfo(buf, " THEN ");
 					get_rule_expr((Node *) when->result, context, true);
 				}