Support UPDATE/DELETE WHERE CURRENT OF cursor_name, per SQL standard.

Along the way, allow FOR UPDATE in non-WITH-HOLD cursors; there may once
have been a reason to disallow that, but it seems to work now, and it's
really rather necessary if you want to select a row via a cursor and then
update it in a concurrent-safe fashion.

Original patch by Arul Shaji, rather heavily editorialized by Tom Lane.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/backend/optimizer/path/tidpath.c b/src/backend/optimizer/path/tidpath.c
index 2470493708a..84564dde734 100644
--- a/src/backend/optimizer/path/tidpath.c
+++ b/src/backend/optimizer/path/tidpath.c
@@ -12,6 +12,12 @@
  * this allows
  *		WHERE ctid IN (tid1, tid2, ...)
  *
+ * We also support "WHERE CURRENT OF cursor" conditions (CurrentOfExpr),
+ * which amount to "CTID = run-time-determined-TID".  These could in
+ * theory be translated to a simple comparison of CTID to the result of
+ * a function, but in practice it works better to keep the special node
+ * representation all the way through to execution.
+ *
  * There is currently no special support for joins involving CTID; in
  * particular nothing corresponding to best_inner_indexscan().	Since it's
  * not very useful to store TIDs of one table in another table, there
@@ -24,7 +30,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/tidpath.c,v 1.29 2007/01/05 22:19:31 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/tidpath.c,v 1.30 2007/06/11 01:16:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -174,6 +180,12 @@ TidQualFromExpr(Node *expr, int varno)
 		if (IsTidEqualAnyClause((ScalarArrayOpExpr *) expr, varno))
 			rlst = list_make1(expr);
 	}
+	else if (expr && IsA(expr, CurrentOfExpr))
+	{
+		/* another base case: check for CURRENT OF on this rel */
+		if (((CurrentOfExpr *) expr)->cvarno == varno)
+			rlst = list_make1(expr);
+	}
 	else if (and_clause(expr))
 	{
 		foreach(l, ((BoolExpr *) expr)->args)