SELECT COUNT(*),COUNT(NVL(comm,0)) FROM emp; 注意空值的影響,以及使用NVL()濾空函數處理空值。
2017-05-07
最后查詢員工的老板的時候,很顯然有漏洞,KING是大BOSS,他沒有老板,但是他也是員工,所以這里需要用自連接加外鏈接,不知道我說的對不對
2017-04-28
SELECT CI_ID,GROUP_CONCAT(STU_NAME) AS STU_NAME FROM
(SELECT p.CI_ID,s.STU_NAME
FROM pm_ci p , pm_stu s
WHERE FIND_IN_SET(s.STU_ID,p.STU_IDS)) AS n
GROUP BY CI_ID;
/*mysql版本*/
(SELECT p.CI_ID,s.STU_NAME
FROM pm_ci p , pm_stu s
WHERE FIND_IN_SET(s.STU_ID,p.STU_IDS)) AS n
GROUP BY CI_ID;
/*mysql版本*/