Filter optimization can cause exception or internal server error in case when a filter condition in WHERE clause is not explicitly boolean expression

Detail name	Value
Changelog Number	22885
Type	Bug
Status	Resolved
Affected Versions	Exasol 8.32.0
Fix Versions	Exasol 8.33.0
Resolution Date	2025-02-27

Description

Since database version 8.32.0 some queries that worked in version 8.31.0 now fail and return one of the following errors:

• more than one column in select list of correlated subselect
• GROUP BY in correlated subselect
• internal server error

Root cause

The issue arises due to filter optimization in the following scenarios:

• When a filter condition in the WHERE clause can be pushed down to a sub-select.
• When the filter condition is not explicitly a Boolean expression, but rather a column that can be of Boolean type, though not necessarily required to be.

Example

create table A (A1 int,A2 int);
insert into A values (1, 1);

select A1 from (select min(true) as abool, A1 from A  group by 2) where abool;

Workaround

Affected queries contain at least one condition in a WHERE , which names a column. This expression has to be extended with = true.

create table A (A1 int,A2 int);
insert into A values (1, 1);

select A1 from (select min(true) as abool, A1 from A  group by 2) where abool=true

Fix

The affected queries will run again without needing the workaround.