Implement SEMI and ANTI joins in the planner and executor. (Semijoins replace

[postgresql] / src / backend / nodes / list.c

diff --git a/src/backend/nodes/list.c b/src/backend/nodes/list.c
index ab54d9aa5954133e67ed0a9013f991faa8ac7e38..4f1819b987459daa01736e4b3457bea54afb84d9 100644 (file)
--- a/src/backend/nodes/list.c
+++ b/src/backend/nodes/list.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/nodes/list.c,v 1.69 2008/01/01 19:45:50 momjian Exp $
+ *       $PostgreSQL: pgsql/src/backend/nodes/list.c,v 1.70 2008/08/14 18:47:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -783,6 +783,42 @@ list_union_oid(List *list1, List *list2)
        return result;
 }
 
+/*
+ * Return a list that contains all the cells that are in both list1 and
+ * list2.  The returned list is freshly allocated via palloc(), but the
+ * cells themselves point to the same objects as the cells of the
+ * input lists.
+ *
+ * Duplicate entries in list1 will not be suppressed, so it's only a true
+ * "intersection" if list1 is known unique beforehand.
+ *
+ * This variant works on lists of pointers, and determines list
+ * membership via equal().  Note that the list1 member will be pointed
+ * to in the result.
+ */
+List *
+list_intersection(List *list1, List *list2)
+{
+       List       *result;
+       ListCell   *cell;
+
+       if (list1 == NIL || list2 == NIL)
+               return NIL;
+
+       Assert(IsPointerList(list1));
+       Assert(IsPointerList(list2));
+
+       result = NIL;
+       foreach(cell, list1)
+       {
+               if (list_member(list2, lfirst(cell)))
+                       result = lappend(result, lfirst(cell));
+       }
+
+       check_list_invariants(result);
+       return result;
+}
+
 /*
  * Return a list that contains all the cells in list1 that are not in
  * list2. The returned list is freshly allocated via palloc(), but the