mysql高级语法

我们一个月前来到优越国际，进入一个班叫xx

SELECT * FROM emp GROUP BY deptno/*分组查询*/

SELECT deptno,sum(sal) FROM emp GROUP BY deptno/*分组查询各个小组的获取金额总数(group by 无太大意义)*/


SELECT emp.empno,emp.ename,emp.sal,emp.deptno,dept.dname,dept.loc FROM emp INNER JOIN dept  on emp.deptno=dept.deptno/*在两个表里相同的deptno字段的基础上连接两个表里的字段*/

SELECT e.*,d.* FROM emp e,dept d WHERE e.deptno=d.deptno/*第二种那个写法*/

SELECT xin.*,d.dname FROM (SELECT deptno,sum(sal) FROM  emp GROUP BY deptno) as xin INNER JOIN dept d ON xin.deptno = d.deptno;/*两个表里的字段连接到一个表里*/




SELECT deptno,sum(sal) FROM  emp GROUP BY deptno;/*各个小组的工资的总和*/


SELECT xin.deptno 部门编号,d.dname 部门名称,xin.sum 总数,xin.count 人数 
FROM (SELECT deptno,SUM(sal) sum,COUNT(empno) count,avg(sal) avg,MAX(sal) max,MIN(sal) min FROM emp GROUP BY deptno) xin ,dept d WHERE xin.deptno = d.deptno/*名称求值*/

SELECT deptno,CONCAT(empno),SUM(sal),AVG(sal) avg_sal FROM  emp GROUP BY deptno HAVING avg_sal BETWEEN 2000 AND 2500/*求平均值之间*/

select * from 表名 limit 0，5/*如果要取第一条数据到第5条就是*/