您可以在from子句中使用子查询：
SELECt S1.TOTAL - S2.TOTALFROM (SELECt (BASICPAY + SUDANG) as TOTAL FROM (SELECt T2.*, ROWNUM AS RN FROM (SELECt T.* FROM TBLINSA T WHERe SUBSTr(T.SSN, 8, 1) = 1 ORDER BY BASICPAY + SUDANG DESC )T 2) T3 WHERe RN = 3 ) S1 CROSS JOIN (SELECt (BASICPAY + SUDANG) AS TOTAL FROM (SELECt T2.*, ROWNUM AS RN FROM (SELECt T.* FROM TBLINSA T WHERe SUBSTr(T.SSN, 8, 1) = 2 ORDER BY BASICPAY + SUDANG DESC ) T2 ) T3 WHERe RN = 9 ) S2
