MySQL表关联的常用方式

发布时间：2023-11-10 16:47:20 所属栏目：MySql教程来源：

导读：建表及插入数据，

CREATE TABLE school (

sch_id int(11) NOT NULL AUTO_INCREMENT,

sch_name varchar(50) NOT NULL,

sch_addr varchar(100) DEFAULT NULL,

PRIMARY KEY (sch_id)

) ENGINE

建表及插入数据，

CREATE TABLE school (

sch_id int(11) NOT NULL AUTO_INCREMENT,

sch_name varchar(50) NOT NULL,

sch_addr varchar(100) DEFAULT NULL,

PRIMARY KEY (sch_id)

) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;

CREATE TABLE student (

st_id int(11) NOT NULL AUTO_INCREMENT,

st_name varchar(20) NOT NULL,

age smallint(6) DEFAULT NULL,

hight int(5) DEFAULT NULL,

sch_id int(11) DEFAULT NULL,

PRIMARY KEY (st_id),

KEY sch_id (sch_id)

) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8 ;

INSERT INTO school VALUES (1,'南开大学','南开'),(2,'中央财经大学','北京'),(3,'香港理工大学','香港'),(4,'西安交通大学','西安'),(5,'悉尼大学','悉尼'),(6,'曼彻斯特大学','曼彻斯特'),(8,'延安抗日军政大学','延安');

INSERT INTO student VALUES (1,'王晓阳',26,168,6),(2,'王楠',28,162,2),(3,'杨振宇',30,178,1),(4,'苗昕',28,162,3),(5,'张诗雨',27,171,5),(8,'李倩',28,162,4),(9,'蒋结石',26,178,7);

1.左关联：以左表为中心，查出左表的全部数据，关联字段值不相等则右表查出的数据显示为空；

select * from school a left join student b on a.sch_id=b.sch_id;

2.右关联：以右表为中心，查出右表的全部数据，关联字段值不相等则左表查出的数据显示为空；

select * from school a right join student b on a.sch_id=b.sch_id;

3.内关联：查出两表关联字段等值的数据

select * from school a inner join student b on a.sch_id=b.sch_id;

4.查出只属于左表的数据

select * from school a left join student b on a.sch_id=b.sch_id where b.st_id is null;

5.查出只属于右表的数据

select * from school a right join student b on a.sch_id=b.sch_id where a.sch_id is null;

6.查出全部数据

select from school a left join student b on a.sch_id=b.sch_id union select from school a right join student b on a.sch_id=b.sch_id;

7.查出左表和右表关联不相等的数据

select from school a left join student b on a.sch_id=b.sch_id where b.st_id is null union select from school a right join student b on a.sch_id=b.sch_id where a.sch_id is null;

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