SQL语句之函数

 1 # 打印入职年份
 2 SELECT ename,DATE_FORMAT(hiredate,"%Y") AS year FROM t_emp;
 3 # 查询1981年上半年入职的员工
 4 SELECT empno,ename,hiredate FROM t_emp WHERE DATE_FORMAT(hiredate,"%Y")=1981 AND DATE_FORMAT(hiredate,"%m")<=6;
 5 # 条件函数－＞中秋节发放礼品，SALES部门发放A，其余部门发放B
 6 SELECT e.ename,d.dname,IF(d.dname="SALES","A","B") AS gift FROM t_emp e JOIN t_dept d ON e.deptno=d.deptno ORDER BY d.deptno;
 7 # SALES部门去北京旅游，RESEARCH部门去上海旅游，ACCOUNTING部门去桂林旅游
 8 SELECT e.ename,d.dname,(CASE WHEN d.dname="SALES" THEN "BEIJING" WHEN d.dname="RESEARCH" THEN "SHANGHAI" ELSE "GUILIN" END) AS loc FROM t_emp e JOIN t_dept d ON e.deptno=d.deptno ORDER BY d.dname;
 9 # 贼多贼多条件的数据更新
10 UPDATE t_emp e LEFT JOIN t_dept d ON e.deptno=d.deptno JOIN (SELECT deptno,AVG(sal) avg FROM t_emp GROUP BY deptno) t ON e.deptno=d.deptno SET e.sal=
11 (CASE
12 WHEN d.dname="SALES" AND DATEDIFF(NOW(),e.hiredate)/365>=20 THEN e.sal*(1+0.1)
13 WHEN d.dname="SALES" AND DATEDIFF(NOW(),e.hiredate)/365<20 THEN e.sal*(1+0.05)
14 WHEN d.dname="ACCOUNTING" THEN e.sal+300
15 WHEN d.dname="RESEARCH" AND e.sal<t.avg THEN e.sal+200
16 WHEN e.deptno IS NULL THEN e.sal+100
17 ELSE NULL
18 END)