Virtual Schema pushdown response with scalar subselect fails

Detail name	Value
Changelog Number	21994
Type	Bug
Status	Resolved
Affected Versions	Exasol 8.6.0
Fix Versions	Exasol 8.33.0, Exasol 8.29.6
Resolution Date	2025-01-14

Description

When Virtual Schema pushdown response contains a scalar subselect, it can lead to an “Internal server error”.

Preparation

create schema test;
--/
CREATE OR REPLACE LUA ADAPTER SCRIPT test.vs_adapter AS
cjson = require "cjson"
function adapter_call( json_req )
req = cjson.decode( json_req )
req.capabilities = {''}
req.schemaMetadata = { tables = {{ name = 'T', columns = {{ name = 'C', dataType = { type = 'BOOLEAN' }}}}}}
req.sql = "SELECT (SELECT TRUE)"
return cjson.encode( req )
end
/
;
CREATE VIRTUAL SCHEMA test_vs USING test.vs_adapter;

Example

SELECT * FROM test_vs.t;

Workaround

No workaround.

Fix

Query runs as expected.