Fix reporting of column typmods for multi-row VALUES constructs.

expandRTE() and get_rte_attribute_type() reported the exprType() and
exprTypmod() values of the expressions in the first row of the VALUES as
being the column type/typmod returned by the VALUES RTE.  That's fine for
the data type, since we coerce all expressions in a column to have the same
common type.  But we don't coerce them to have a common typmod, so it was
possible for rows after the first one to return values that violate the
claimed column typmod.  This leads to the incorrect result seen in bug
#14448 from Hassan Mahmood, as well as some other corner-case misbehaviors.

The desired behavior is the same as we use in other type-unification
cases: report the common typmod if there is one, but otherwise return -1
indicating no particular constraint.  It's cheap for transformValuesClause
to determine the common typmod while transforming a multi-row VALUES, but
it'd be less cheap for expandRTE() and get_rte_attribute_type() to
re-determine that info every time they're asked --- possibly a lot less
cheap, if the VALUES has many rows.  Therefore, the best fix is to record
the common typmods explicitly in a list in the VALUES RTE, as we were
already doing for column collations.  This looks quite a bit like what
we're doing for CTE RTEs, so we can save a little bit of space and code by
unifying the representation for those two RTE types.  They both now share
coltypes/coltypmods/colcollations fields.  (At some point it might seem
desirable to populate those fields for all RTE types; but right now it
looks like constructing them for other RTE types would add more code and
cycles than it would save.)

The RTE change requires a catversion bump, so this fix is only usable
in HEAD.  If we fix this at all in the back branches, the patch will
need to look quite different.

Report: https://postgr.es/m/20161205143037.4377.60754@wrigleys.postgresql.org
Discussion: https://postgr.es/m/27429.1480968538@sss.pgh.pa.us

1 files changed, 11 insertions, 4 deletions

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 6b95c484476..fc532fbd432 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -927,7 +927,6 @@ typedef struct RangeTblEntry
 	 * Fields valid for a values RTE (else NIL):
 	 */
 	List	   *values_lists;	/* list of expression lists */
-	List	   *values_collations;		/* OID list of column collation OIDs */
 
 	/*
 	 * Fields valid for a CTE RTE (else NULL/zero):
@@ -935,9 +934,17 @@ typedef struct RangeTblEntry
 	char	   *ctename;		/* name of the WITH list item */
 	Index		ctelevelsup;	/* number of query levels up */
 	bool		self_reference; /* is this a recursive self-reference? */
-	List	   *ctecoltypes;	/* OID list of column type OIDs */
-	List	   *ctecoltypmods;	/* integer list of column typmods */
-	List	   *ctecolcollations;		/* OID list of column collation OIDs */
+
+	/*
+	 * Fields valid for values and CTE RTEs (else NIL):
+	 *
+	 * We need these for CTE RTEs so that the types of self-referential
+	 * columns are well-defined.  For VALUES RTEs, storing these explicitly
+	 * saves having to re-determine the info by scanning the values_lists.
+	 */
+	List	   *coltypes;		/* OID list of column type OIDs */
+	List	   *coltypmods;		/* integer list of column typmods */
+	List	   *colcollations;	/* OID list of column collation OIDs */
 
 	/*
 	 * Fields valid in all RTEs: