mysql_连表查询

Posted 2021-03-11 手可摘星辰。

1.内连接（只取两张表的共同部分）

# 将表employee 和 department 的相同部分根据employee表中的dep_id字段和department表中的id字段连接起来。
select * from employee inner join department on employee.dep_id = department.id;

2.左连接（在内连接的基础上保留左边表的记录）

select * from employee left join department on employee.dep_id = department.id;

3.右连接（在内连接的基础上保留右边表的记录）

select * from employee right join department on employee.dep_id = department.id;

4.全外连接（保留左右两表没有对应关系的记录）

# 将左连接和右连接查出来的记录和在一起，再去重~
select * from employee left join department on employee.dep_id = department.id union select * from employee right join department on employee.dep_id = department.id;

 

#示例1：以内连接的方式查询employee和department表，并且employee表中的age字段值必须大于25,即找出年龄大于25岁的员工以及员工所在的部门
select employee.name,department.name from employee inner join department on employee.dep_id = department.id where age > 25;

#示例2：以内连接的方式查询employee和department表，并且以age字段的升序方式显示
select * from employee inner join department on employee.dep_id = department.id order by age asc;