SELECT COUNT(*)，SUM(SAL) FROM EMP WHERE DEPT_NO = 0020 AND ENAME LIKE ‘SMITH%';
SELECT COUNT(*)，SUM(SAL) FROM EMP WHERE DEPT_NO = 0030 AND ENAME LIKE ‘SMITH%';
你可以用DECODE函數高效地得到相同結果
SELECT COUNT(DECODE(DEPT_NO,0020,'X',NULL)) D0020_COUNT, COUNT(DECODE(DEPT_NO,0030,'X',NULL)) D0030_COUNT, SUM(DECODE(DEPT_NO,0020,SAL,NULL)) D0020_SAL, SUM(DECODE(DEPT_NO,0030,SAL,NULL)) D0030_SAL FROM EMP WHERE ENAME LIKE ‘SMITH%';
類似的,DECODE函數也可以運用于GROUP BY 和ORDER BY子句中.
9. 整合簡單,無關聯的數據庫訪問
如果你有幾個簡單的數據庫查詢語句,你可以把它們整合到一個查詢中(即使它們之間沒有關系)
例如:
SELECT NAME FROM EMP WHERE EMP_NO = 1234;
SELECT NAME FROM DPT WHERE DPT_NO = 10 ;
SELECT NAME FROM CAT WHERE CAT_TYPE = ‘RD';
上面的3個查詢可以被合并成一個:
SELECT E.NAME , D.NAME , C.NAME FROM CAT C , DPT D , EMP E,DUAL X WHERE NVL(‘X',X.DUMMY) = NVL(‘X',E.ROWID(+)) AND NVL(‘X',X.DUMMY) = NVL(‘X',D.ROWID(+)) AND NVL(‘X',X.DUMMY) = NVL(‘X',C.ROWID(+)) AND E.EMP_NO(+) = 1234 AND D.DEPT_NO(+) = 10 AND C.CAT_TYPE(+) = ‘RD';
