Mysql表的内联和外联区别案例解析

select 字段 from 表1 inner join 表2 on 连接条件 and 其他条件；

mysql> select ename, dname from emp, dept where emp.deptno=dept.deptno and ename='SMITH';
+-------+----------+
| ename | dname    |
+-------+----------+
| SMITH | RESEARCH |
+-------+----------+
1 row in set (0.00 sec)

mysql> select ename, dname from emp inner join dept on emp.deptno=dept.deptno and ename='SMITH';
+-------+----------+
| ename | dname    |
+-------+----------+
| SMITH | RESEARCH |
+-------+----------+
1 row in set (0.00 sec)

mysql> select ename, dname from emp inner join dept on emp.deptno=dept.deptno where ename='SMITH';
+-------+----------+
| ename | dname    |
+-------+----------+
| SMITH | RESEARCH |
+-------+----------+
1 row in set (0.00 sec)

select 字段名 from 表名1 left join 表名2 on 连接条件

mysql> create table stu (id int, name varchar(30));-- 学生表
Query OK, 0 rows affected (0.03 sec)
mysql> desc stu;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into stu values(1,'jack'),(2,'tom'),(3,'kity'),(4,'nono');
Query OK, 4 rows affected (0.01 sec)
Records: 4  Duplicates: 0  Warnings: 0
mysql> select * from stu;
+------+------+
| id   | name |
+------+------+
|    1 | jack |
|    2 | tom  |
|    3 | kity |
|    4 | nono |
+------+------+
4 rows in set (0.00 sec)
mysql> create table exam (id int, grade int); -- 成绩表
Query OK, 0 rows affected (0.02 sec)
mysql> desc exam;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | YES  |     | NULL    |       |
| grade | int(11) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into exam values(1, 56),(2,76),(11, 8);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> select * from exam;
+------+-------+
| id   | grade |
+------+-------+
|    1 |    56 |
|    2 |    76 |
|   11 |     8 |
+------+-------+
3 rows in set (0.00 sec)

mysql> select * from stu left join exam on stu.id=exam.id;
+------+------+------+-------+
| id   | name | id   | grade |
+------+------+------+-------+
|    1 | jack |    1 |    56 |
|    2 | tom  |    2 |    76 |
|    3 | kity | NULL |  NULL |
|    4 | nono | NULL |  NULL |
+------+------+------+-------+
4 rows in set (0.00 sec)

select 字段 from 表名1 right join 表名2 on 连接条件；

mysql> select * from stu right join exam on stu.id=exam.id;
+------+------+------+-------+
| id   | name | id   | grade |
+------+------+------+-------+
|    1 | jack |    1 |    56 |
|    2 | tom  |    2 |    76 |
| NULL | NULL |   11 |     8 |
+------+------+------+-------+
3 rows in set (0.00 sec)

mysql> select dept.deptno, dname, ename from  dept left join emp on dept.deptno=emp.deptno order by dept.deptno asc;
+--------+------------+--------+
| deptno | dname      | ename  |
+--------+------------+--------+
|     10 | ACCOUNTING | CLARK  |
|     10 | ACCOUNTING | MILLER |
|     10 | ACCOUNTING | KING   |
|     20 | RESEARCH   | JONES  |
|     20 | RESEARCH   | SMITH  |
|     20 | RESEARCH   | ADAMS  |
|     20 | RESEARCH   | SCOTT  |
|     20 | RESEARCH   | FORD   |
|     30 | SALES      | MARTIN |
|     30 | SALES      | ALLEN  |
|     30 | SALES      | JAMES  |
|     30 | SALES      | BLAKE  |
|     30 | SALES      | WARD   |
|     30 | SALES      | TURNER |
|     40 | OPERATIONS | NULL   |
+--------+------------+--------+
15 rows in set (0.00 sec)

mysql> select dept.deptno, dname, ename from emp right join dept on dept.deptno=emp.deptno order by dept.deptno asc;
+--------+------------+--------+
| deptno | dname      | ename  |
+--------+------------+--------+
|     10 | ACCOUNTING | CLARK  |
|     10 | ACCOUNTING | MILLER |
|     10 | ACCOUNTING | KING   |
|     20 | RESEARCH   | JONES  |
|     20 | RESEARCH   | SMITH  |
|     20 | RESEARCH   | ADAMS  |
|     20 | RESEARCH   | SCOTT  |
|     20 | RESEARCH   | FORD   |
|     30 | SALES      | MARTIN |
|     30 | SALES      | ALLEN  |
|     30 | SALES      | JAMES  |
|     30 | SALES      | BLAKE  |
|     30 | SALES      | WARD   |
|     30 | SALES      | TURNER |
|     40 | OPERATIONS | NULL   |
+--------+------------+--------+
15 rows in set (0.00 sec)