Fix UNION/INTERSECT/EXCEPT so that when two inputs being merged have

same data type and same typmod, we show that typmod as the output
typmod, rather than generic -1.  This responds to several complaints
over the past few years about UNIONs unexpectedly dropping length or
precision info.

4 files changed, 15 insertions, 4 deletions

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 1d7e20c1e8b..fc618f72d1c 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.150 2006/08/02 01:59:45 joe Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.151 2006/08/10 02:36:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -813,6 +813,10 @@ recurse_pushdown_safe(Node *setOp, Query *topquery,
  * Compare tlist's datatypes against the list of set-operation result types.
  * For any items that are different, mark the appropriate element of
  * differentTypes[] to show that this column will have type conversions.
+ *
+ * We don't have to care about typmods here: the only allowed difference
+ * between set-op input and output typmods is input is a specific typmod
+ * and output is -1, and that does not require a coercion.
  */
 static void
 compare_tlist_datatypes(List *tlist, List *colTypes,
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 856181d090d..2fe78473048 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.39 2006/07/14 14:52:21 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.40 2006/08/10 02:36:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -716,6 +716,7 @@ is_simple_union_all_recurse(Node *setOp, Query *setOpQuery, List *colTypes)
 		Assert(subquery != NULL);
 
 		/* Leaf nodes are OK if they match the toplevel column types */
+		/* We don't have to compare typmods here */
 		return tlist_same_datatypes(subquery->targetList, colTypes, true);
 	}
 	else if (IsA(setOp, SetOperationStmt))
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 3b9e740cadf..3bf7223199f 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -22,7 +22,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.132 2006/04/30 18:30:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.133 2006/08/10 02:36:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -152,6 +152,10 @@ plan_set_operations(PlannerInfo *root, double tuple_fraction,
  * flag: if >= 0, add a resjunk output column indicating value of flag
  * refnames_tlist: targetlist to take column names from
  * *sortClauses: receives list of SortClauses for result plan, if any
+ *
+ * We don't have to care about typmods here: the only allowed difference
+ * between set-op input and output typmods is input is a specific typmod
+ * and output is -1, and that does not require a coercion.
  */
 static Plan *
 recurse_set_operations(Node *setOp, PlannerInfo *root,
diff --git a/src/backend/optimizer/util/tlist.c b/src/backend/optimizer/util/tlist.c
index c75c496065c..74ebb3fc24b 100644
--- a/src/backend/optimizer/util/tlist.c
+++ b/src/backend/optimizer/util/tlist.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.72 2006/03/05 15:58:32 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.73 2006/08/10 02:36:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -174,6 +174,8 @@ get_sortgrouplist_exprs(List *sortClauses, List *targetList)
  *
  * Resjunk columns are ignored if junkOK is true; otherwise presence of
  * a resjunk column will always cause a 'false' result.
+ *
+ * Note: currently no callers care about comparing typmods.
  */
 bool
 tlist_same_datatypes(List *tlist, List *colTypes, bool junkOK)