Query with UNION, CTE and LIMIT fails due to "insertion limit"

Detail name	Value
Changelog Number	17644
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 a LIMIT clause.

Example

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

Workaround

Wrap a select around the first table operand:

-- Observed: The query succeeds.
SELECT *
FROM ( WITH cte AS ( SELECT 1 AS c )
       SELECT 1 )
UNION
SELECT 1 LIMIT 1;

Fix

The query succeeds.