SQL语句之DELETE

Posted 2021-03-05 萌新想吃鱼

 1 # 删除10部门里面，工龄超过20年的员工记录
 2 DELETE IGNORE FROM t_emp WHERE deptno=10 AND DATEDIFF(NOW(),hiredate)/365>=20;
 3 # 删除20部门里面工资最高的纪录
 4 DELETE IGNORE FROM t_emp WHERE deptno=20 ORDER BY sal DESC LIMIT 1;
 5 # 删除SALES部门和该部门的所有员工记录
 6 DELETE e,d FROM t_emp e JOIN t_dept d ON e.deptno=d.deptno WHERE d.dname="SALES";
 7 # 删除每个低于部门平均底薪的员工记录
 8 DELETE e FROM t_emp e JOIN (SELECT deptno,AVG(sal) avg FROM t_emp GROUP BY deptno) t ON e.deptno=t.deptno WHERE sal<avg;
 9 # 删除员工KING和他直接下属的记录
10 DELETE e FROM t_emp e JOIN (SELECT empno FROM t_emp WHERE ename="KING") t ON e.mgr=t.empno OR e.empno=t.empno;
11 # 删除SALES部门的员工及没有部门的员工
12 DELETE e FROM t_emp e LEFT JOIN t_dept d ON e.deptno=d.deptno WHERE d.dname="SALES" OR e.deptno IS NULL;
13 # 绕过事务机制直接删除全表数据
14 TRUNCATE TABLE t_emp;