mysql查询之内连接查询

mysql> select * from dept;
+--------+--------+------+
| deptnu | dname  | addr |
+--------+--------+------+
| 1      | 董事会 | 北京 |
| 2      | 决策部 | 北京 |
| 3      | 行政部 | 北京 |
| 4      | 销售部 | 上海 |
+--------+--------+------+
4 rows in set


mysql> select * from employee;
+-------+-------+--------+------------+--------+--------+
| empno | ename | job    | hiredate   | sal    | deptnu |
+-------+-------+--------+------------+--------+--------+
| 10000 | tom   | 董事长 | 2020-05-10 | 100000 | 1      |
| 10001 | jerry | CEO    | 2020-05-10 | 80000  | 2      |
| 10002 | 张三  | 经理   | 2020-05-10 | 70000  | 3      |
| 10003 | 李四  | 经理   | 2020-05-10 | 70000  | 3      |
| 10004 | 王五  | 销售   | 2020-05-10 | 70000  | 4      |
| 10005 | 赵六  | 销售   | 2020-05-10 | 70000  | 4      |
+-------+-------+--------+------------+--------+--------+
6 rows in set


### 查出员工赵六所在部门的地址
mysql> select d.addr from dept d inner join employee e on d.deptnu = e.deptnu and e.ename = '赵六';
+------+
| addr |
+------+
| 上海 |
+------+
1 row in set


###推荐此查询用法，查询效率比上面高
mysql> select d.addr from dept d,employee e where d.deptnu = e.deptnu and e.ename = '赵六';
+------+
| addr |
+------+
| 上海 |
+------+
1 row in set