I'm trying to use SQLAlchemy to generate a query that involves both CTEs and a union. Unfortunately whenever I apply a union the generated SQL does not include the defined CTE.
Here's the SQL including the WITH, without a UNION:
(Pdb) import sqlalchemy as sa
(Pdb) print str(sa.select([sa.select([sa.sql.null().label('a1')]).cte('bb')]))
WITH bb AS
(SELECT NULL AS a1)
SELECT bb.a1
FROM bb
Now the same query but with a call to union:
(Pdb) print str(sa.select([sa.select([sa.sql.null().label('a1')]).cte('bb')]).union_all(sa.select([sa.sql.null().label('b1')])))
SELECT bb.a1
FROM bb UNION ALL SELECT NULL AS b1
I'd expect the query with the union call to still include the WITH, but it does not.
I do believe this is a bug. I applied the following patch to make UNIONs work with CTEs:
--- sqlalchemy.orig/sql/compiler.py 2012-05-20 17:39:41.000000000 +0000
+++ sqlalchemy/sql/compiler.py 2012-05-20 17:39:00.000000000 +0000
@@ -562,6 +562,15 @@
text += (cs._limit is not None or cs._offset is not None) and \
self.limit_clause(cs) or ""
+ if self.ctes and \
+ compound_index==1 and not entry:
+ cte_text = self.get_cte_preamble(self.ctes_recursive) + " "
+ cte_text += ", \n".join(
+ [txt for txt in self.ctes.values()]
+ )
+ cte_text += "\n "
+ text = cte_text + text
+
self.stack.pop(-1)
if asfrom and parens:
return "(" + text + ")"
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