GROUP BY in CTE causes ELSE in outer query to be prematurely evaluated

Hi

If you have the query

WITH FOO AS (
SELECT 0 AS GROUPING
)
SELECT CASE
WHEN GROUPING >= 0 THEN 'non-negative'
ELSE CAST((1 / 0) AS VARCHAR)
END
FROM FOO;

it works successfully, having the ELSE as a safeguard against having coded
a bug, having forgotten a WHEN branch, so it fails fast.

So if you have

WITH FOO AS (
SELECT -1 AS GROUPING
)
SELECT CASE
WHEN GROUPING >= 0 THEN 'non-negative'
ELSE CAST((1 / 0) AS VARCHAR)
END
FROM FOO;

it fails with a division by zero error.

But if you have the query

WITH FOO AS (
SELECT 0 AS GROUPING
GROUP BY 1
)
SELECT CASE
WHEN GROUPING >= 0 THEN 'non-negative'
ELSE CAST((1 / 0) AS VARCHAR)
END
FROM FOO;

then it always fails with division by zero error, even though the result
should still be 'non-negative'.

Cheers
Björn