mysql数据表的连接实例

mysql数据表之间的连接

本例以student表和teacher表为例；

student：id,name,birthday,sex,goal,tid (id为主键，tid为外键);

teacher: tid,name,sex,birthday;

1. 显示student表中学生的id，name，教师编号，以及教师编号所对应的教师姓名；

student表中和teacher表中name相同必须注明是具体哪个表中的；

select id,student.name,student.tid,teacher.name from student,teacher

where student.tid=teacher.tid;

用别名连接也可以： 别名使用： (表名 别名);

select e.id,e.name,e.tid,d.name from student e,teacher d where e.tid=d.tid;

99年出的自然连接:前面一种在mysql下用不了查出来是空的，后面一种能够查出来！

select e.id, e.name,tid,d.name from student e natural join teacher d;

select e.id,e.name, tid,d.name from student e join teacher d using(tid);

现在常见的用法是：

select e.id,e.name,e.tid,d.name from student e join teacher d on e.tid=d.tid;

2. 成绩高于90的学生编号，姓名，成绩，老师编号，姓名；

select e.id,e.name,e.goal,e.tid,d.name from student e ,teacher d where

e.tid=d.tid and e.goal>90;

select id,student.name,goal,student.tid,teacher.name from student,teacher

where student.tid=teacher.tid and goal>90;

select e.id,e.name,e.goal,e.tid,d.name from student e join teacher d on

e.tid=d.tid and e.goal>90;

3.非等值连接

select e.id,e.name,e.goal,g.level from student e,grade g where e.goal between g.lower and g.heiger;

4. 自连接

select e.id,e.name,m.monitor,m.name from student e,student m where e.monitor=m.id

order m.monitor;

5. 外连接

左连接：(等右叫左，等式右边有加号叫左连接！);

select e.id,e.name,e.goal,e.tid,d.name from student e left join teacher d

on e.tid=d.tid;

右连接：(等左叫右，等式左边有加号叫右连接!)；

select e.id,e.name,e.goal,e.tid,d.name from student e right join teacher

d on e.tid=d.tid;

全连接：mysql 中并不支持全链接，但可以将两个连接合并，可以达到相同的效果

即：左连接 union 右连接

select e.id,e.name,e.goal,e.tid,d.name from student e left join teacher d

on e.tid=d.tid

union

select e.id,e.name,e.goal,e.tid,d.name from student e right join teacher d on e.tid=d.tid;

6. 子查询:

单行子查询:后面的查询必须只有一个结果集！

select id,name,sex ,goal from student where goal>(select goal from

student where name='赵铁刚');

mysql中聚合函数min(),max(),avg(),sum(),count(),不能嵌套使用

通过表链接，from里面加上查询子句

查询每个老师下面的学生的平均成绩，平均成绩要求大于最低平均成绩;

最低平均成绩查询：student1 为每个老师带的学生平均成绩表的别名；

goal1为平均分的别名：

select min(goal1) from (select avg(goal)goal1 from student group by tid) student1;

平局成绩大于最低平均成绩查询：(注意判断条件里面的tid不要在前面加上e.或d.

会导致查询出错Unkonwn e.tid);

select e.tid,d.name,avg(e.goal) from student e join teacher d on e.tid=d.tid group by

e.tid having avg(e.goal)>(select min(goal1) from (select avg(goal) goal1 from student group by tid) student1);

查询与赵铁刚分数相同的人

select id,name,sex,goal from student where goal=(select goal from student where name='赵铁刚');

或者查询与赵铁刚同一个老师的同学；

select id,name,sex,goal,tid from student where tid=(select tid from

student where name='赵铁刚');

多行子查询：any>(大于最小)，any<(小于最大),all>(大于最大),all<(小于最小);

查询分数比最低平均分数低的学生信息 (小于最小的问题)

select id,name,sex,goal from student where goal<(select

min(goal1) from (select avg(goal) goal1 from student group by tid) student1);

用<all也可以

select id,name,sex,goal from student where goal<all(select avg(goal) from student group by tid);

查询不必最低平局分数还低的学生信息

select id,name,sex,goal from student where goal>any(select avg(goal) from student group by tid);

查询不比最高平均分还高的学生信息

select id,name,sex,goal from student where goal<any(select avg(goal)

from student group by tid);

查询比最高分还高的的学生信息

select id,name,sex,goal from student where goal>all(select avg(goal) from student group by tid);

7. limit用法

获取的是前5行的数据

select id,name,sex,goal from student limit 0,5;

8. 差集：

NOT IN 表示差集

SELECT * FROM table1 WHERE name NOT IN (SELECT name FROM table2);

交集：

SELECT * FROM table1 AS a JOIN table2 AS b ON a.name =b.name;