i want to select records between 20 to 30
i used the first n row. The query is as follows

SELECT FIRST 30 user_id FROM a_user WHERE NOT EXISTS( SELECT FIRST 20 user_id FROM a_user)

but first is not supported in subquery.

so i userd temp table,the query is as follows

SELECT FIRST 30 * FROM a_user INTO temp first30;
SELECT FIRST 20 * FROM a_user INTO temp first20;
SELECT user_id FROM first30 WHERE NOT EXISTS ( SELECT user_id FROM first20)

but it does not work,message is same.

Please help me out what is the alternate way