Odd error when using UNION and COLLATE

Seems you can't use UNION and COLLATE in the same SELECT statement; you
have to put the UNION inside of WITH and then do the COLLATE outside:

test=> SELECT 'a-c' AS x UNION ALL SELECT 'ab' AS x ORDER BY 1 COLLATE "C";
ERROR: collations are not supported by type integer
LINE 1: ... 'a-c' AS x UNION ALL SELECT 'ab' AS x ORDER BY 1 COLLATE "C...
^

test=> SELECT 'a-c' AS x UNION ALL SELECT 'ab' AS x ORDER BY x COLLATE "C";
ERROR: invalid UNION/INTERSECT/EXCEPT ORDER BY clause
LINE 1: ...CT 'a-c' AS x UNION ALL SELECT 'ab' AS x ORDER BY x COLLATE ...
^
DETAIL: Only result column names can be used, not expressions or functions.
HINT: Add the expression/function to every SELECT, or move the UNION into a FROM clause.

test=> WITH d AS (SELECT 'a-c' AS x UNION ALL SELECT 'ab' AS x) SELECT * FROM d ORDER BY x COLLATE "C";
x
-----
a-c
ab
(2 rows)

I think the 'ORDER BY x COLLATE "C"' is being parsed as an a_expr, and
we don't allow a_expr in a UNION. Perhaps we are too strict here, but I
can't tell.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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