mysql self-connection query example analysis

1. Self-join query is a special multi-table join query, because the tables of the two related queries are the same table. They are virtualized into two tables by taking aliases and then connected.

2. A self-join query is to connect itself to itself. Give a table two different aliases, and then attach the connection conditions.

Example

#这些数据全部在员工表中
#把t_employee表，即当做员工表，又当做领导表
#领导表是虚拟的概念，我们可以通过取别名的方式虚拟
SELECT employee.id "员工的编号",emp.ename "员工的姓名" ,emp.salary "员工的薪资",
manager.id "领导的编号" ,manager.ename "领导的姓名",manager.salary "领导的薪资"
FROM emp employee INNER JOIN emp manager
#emp employee：employee.，表示的是员工表的
#emp manager：如果用manager.，表示的是领导表的
ON employee.mgr = manager.id  # 员工的mgr指向上级的id
 
#表的别名不要加""，给列取别名，可以用""，列的别名不使用""也可以，但是要避免包含空格等特殊符号。

The above is the detailed content of mysql self-connection query example analysis. For more information, please follow other related articles on the PHP Chinese website!