Database: financial
Question: List out the account numbers of female clients who are oldest and has lowest average salary, calculate the gap between this lowest average salary with the highest average salary?
SQL: SELECT T1.account_id , ( SELECT MAX(A11) - MIN(A11) FROM district ) FROM account AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id INNER JOIN disp AS T3 ON T1.account_id = T3.account_id INNER JOIN client AS T4 ON T3.client_id = T4.client_id WHERE T2.district_id = ( SELECT district_id FROM client WHERE gender = 'F' ORDER BY birth_date ASC LIMIT 1 ) ORDER BY T2.A11 DESC LIMIT 1