"Internal server error" caused by certain NULLIF and simple CASE expressions

Detail name	Value
Changelog Number	32494
Type	Bug
Status	Open
Affected Versions	Exasol 7.0.0, Exasol 8.2.0, Exasol 8.6.0, Exasol 2025.1.0, Exasol 2026.1.0, Exasol 2025.1.16

Description

An “internal server error” could occur during query compilation when a NULLIF expression and a simple CASE expression (CASE <expression> WHEN <value> ...) in the same SQL clause resolved to the same comparison involving a column. This also applied when constant folding made the comparisons equal.

The expressions did not need to be nested; separate select-list expressions could also trigger the error. It could occur with empty tables and across supported column types.

For example:

CREATE TABLE t(c0 varchar(1));

SELECT CASE c0 WHEN c0 THEN NULLIF(c0, c0) END FROM t;

Workaround

No general workaround available.

Fix

Fixed an internal error caused by affected NULLIF and simple CASE expression.