This is not a bug, but a documented feature. list() returns BLOB. And blobs are distict because BLOB_ID-s are compared.
SELECT DISTINCT, ORDER BY and GROUP BY work on the BLOB ID, not the contents. https://firebirdsql.org/refdocs/langrefupd21-blob.html https://firebirdsql.org/refdocs/langrefupd21-blob.html You ust use CAST in this case. with cte as (select 1 cnt from rdb$database union all select 2 from rdb$database ) select cast(list(cnt) as varchar(10)) from cte union select cast(list(cnt) as varchar(10)) from cte
