> I am using Firebird 1.0.3. But when I issue the following SQL
> statement, I always get a invalid column reference error.
>
> SELECT * FROM MEMBERSHIP GROUP BY USERNAME;
>
> But the following run OK
>
> SELECT * FROM MEMBERSHIP ORDER BY USERNAME;
>
> I seems Firebird does not support the GROUP BY. Is it?

GROUP BY needs an aggregate
you need
SELECT FIELD1, SUM(FIELD2) FROM MEMBERSHIP GROUP BY FIELD1
or AVG etc
TO USE GROUP BY
I think this is pretty standard SQL

Alan