日常 MYSQL小结

1，group   by 分组查询  select 字段名(函数) from(表名) group up字段名 having 函数; 

与 函数套用

2， select  表名.字段名 from 表1 inner join 表2 on 表名1.id=表名2.id（字段属性和值相同）

inner join on 链接数据库 右链right join  左链接left jion (附加)

select （表名.属性） from （双表）where （字段属性和值相同）

补充group by 追加链表
SELECT xin.*,dept.dname FROM (SELECT SUM(sal),deptno FROM emp GROUP BY deptno) xin INNER JOIN dept on dept.deptno=xin.deptno;
SELECT xin.*,dept.dname FROM (SELECT SUM(sal),deptno FROM emp GROUP BY deptno) xin,dept WHERE dept.deptno=xin.deptno;
SELECT emp.deptno,SUM(emp.sal),COUNT(emp.empno),dept.dname FROM emp,dept WHERE emp.deptno=dept.deptno GROUP BY deptno
追加having
SELECT SUM(sal),deptno,AVG(sal) FROM emp GROUP BY deptno HAVING AVG(sal) BETWEEN 2000 and 2500