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<>MySQL多表查询语句
<>1.内连接查询
1.隐式内连接：使用where条件消除无用数据 例子： --查询所有员工信息和对应的部门信息 SELECT * FROM emp,dept WHERE emp
.dept_id=dept.id; --查询员工表的姓名，性别，部门表的名称 SELECT t1.name, -- 员工表姓名 t1.gender, --
员工表性别 t2.name -- 部门表名称 FROM emp t1, dept t2 WHERE t1.dept_id=t2.id; 2.显示内连接
语法：select 字段列表 from 表名1 [inner] join 表名2 on 条件 例子： SELECT * FROM emp INNER JOIN
deptON emp.dept_id=dept.id; SELECT * FROM emp JOIN dept ON emp.dept_id=dept.id;
<>2.外连接查询：
1.左外连接： 语法：select 字段列表 from 表1 left [outer] join 表2 on 条件； 查询的是左表所有数据以及其交集部分
例子： SELECT t1.*,t2.name FROM emp t1 LEFT JOIN dept t2 ON t1.dept_id = t2.id; 2.
右外连接： 语法：select 字段列表 from 表1 right [outer] join 表2 on 条件； 查询的是右表所有数据以及其交集部分 例子：
SELECT t1.*,t2.name FROM dept t2 RIGHT JOIN emp t1 ON t1.dept_id = t2.id;
