20.用表跟尾交流EXISTS
屡屡来说，给与表跟尾的编制比EXISTS更有效率
SELECT ENAME
FROM EMP E
WHERE EXISTS (SELECT ‘X’
FROM DEPT
WHERE DEPT_NO = E.DEPT_NO
AND DEPT_CAT = ‘A&a
20.用表跟尾交流EXISTS
屡屡来说，给与表跟尾的编制比EXISTS更有效率
SELECT ENAME
FROM EMP E
WHERE EXISTS (SELECT ‘X’
FROM DEPT
WHERE DEPT_NO = E.DEPT_NO
AND DEPT_CAT = ‘A&a