Wrong column names in UNION ALL

Detail name	Value
Changelog Number	11195
Type	Bug
Status	Resolved
Affected Versions	Exasol 6.1.0, EXASOL 6.0.10, Exasol 6.2.0, Exasol 7.0.0
Fix Versions	Exasol 7.1.0, Exasol 7.0.11
Resolution Date	2021-07-16

Description

Statements using UNION or UNION ALL may ignore column aliases in some cases.

Preparation

CREATE TABLE table_one (A VARCHAR(2000));
CREATE TABLE table_two (B VARCHAR(2000));

Example

select A as C from table_one
UNION ALL
select B as C from table_two;

Shows column name A instead of C

Workaround

You can wrap the UNION ALL statement in a subselect with a column alias:

select A as C 
from 
(
SELECT A FROM table_one
UNION ALL
SELECT B FROM table_two
);

Fix

UNION and UNION ALL will always respect column aliases