Internal error on UNION with CTE and ORDER BY FALSE

Detail name	Value
Changelog Number	26960
Type	Bug
Status	Resolved
Affected Versions	Exasol 7.1.0, Exasol 8.0.0, Exasol 8.29.0, Exasol 2025.1.0, Exasol 2025.2.0
Fix Versions	Exasol 2026.1.0, Exasol 2025.2.1
Resolution Date	2026-03-20

Description

A query with the following conditions can crash:

• There is a UNION or UNION ALL.
• The first table operand has parentheses and a Common Table Expression (CTE, WITH clause).
• The last table operand has ORDER BY FALSE.

Example

-- Observed: The query fails with "Internal server error"
(
  WITH cte AS ( SELECT 1 AS c )
  SELECT 1
)
UNION
SELECT 1 ORDER BY FALSE;

Workaround

Wrap a select around the first table operand.

Before Improvement CHANGELOG: ORDER BY FALSE with table operators ORDER BY FALSE in table operators (UNION, UNION ALL, INTERSECT, EXCEPT) wasn’t allowed, so the original query shouldn’t have been crashing (“Internal Server Error”), but failing with error "order by object not found".

-- Observed: The query fails with the error "order by object not found".
SELECT *
FROM ( WITH cte AS ( SELECT 1 AS c )
       SELECT 1 )
UNION
SELECT 1 ORDER BY FALSE;

Fix

The query succeeds.