文件名称：MySQL数据库优化SQL
文件大小：879KB
文件格式：PPT
更新时间：2021-07-09 09:19:17
MySQL优化
MySQL数据库优化SQL20、查询显示每个雇员加入公司的准确时间，按××××年××月××日 时分秒显示； select ename, to_char(hiredate, 'yyyy-mm-dd hh24:mi:ss') from emp; 21、查询公司中按年份月份统计各地的录用职工数量 select d.loc, count(1) "录用人数" from emp e join dept d on e.deptno=d.deptno group by to_char(hiredate,'yyyy'), to_char(hiredate,'mm'); 22、查询列出各部门的部门名和部门经理名字 select d.deptno, d.dname, e.ename from dept d join emp e on d.deptno=e.deptno where e.job='MANAGER'; 23、查询部门平均工资最高的部门名称和最低的部门名称 select dname from dept where deptno = (select deptno from emp group by deptno having avg(sal) = (select max(avg(sal)) from emp group by deptno)); select dname from dept where deptno = (select deptno from emp group by deptno having avg(sal) = (select max(avg(sal)) from emp group by deptno)) union select dname from dept where deptno = (select deptno from emp group by deptno having avg(sal) = (select min(avg(sal)) from emp group by deptno))