MySQL表中的连接方式其实非常简单，这里就简单的罗列出他们的特点。

表的连接（JOIN）可以分为内连接（JOIN/INNER JOIN）和外连接（LEFT JOIN/RIGHT JOIN）。

首先我们看一下我们本次演示的两个表：

mysql> SELECT * FROM student;+------+----------+------+------+| s_id | s_name  | age | c_id |+------+----------+------+------+|  1 | xiaoming |  13 |  1 ||  2 | xiaohong |  41 |  4 ||  3 | xiaoxia |  22 |  3 ||  4 | xiaogang |  32 |  1 ||  5 | xiaoli  |  41 |  2 ||  6 | wangwu  |  13 |  2 ||  7 | lisi   |  22 |  3 ||  8 | zhangsan |  11 |  9 |+------+----------+------+------+8 rows in set (0.00 sec)mysql> SELECT * FROM class;+------+---------+-------+| c_id | c_name | count |+------+---------+-------+|  1 | MATH  |  65 ||  2 | CHINESE |  70 ||  3 | ENGLISH |  50 ||  4 | HISTORY |  30 ||  5 | BIOLOGY |  40 |+------+---------+-------+5 rows in set (0.00 sec)

1.内连接

mysql> SELECT * FROM student INNER JOIN class ON student.c_id = class.c_id;+------+----------+------+------+------+---------+-------+| s_id | s_name  | age | c_id | c_id | c_name | count |+------+----------+------+------+------+---------+-------+|  1 | xiaoming |  13 |  1 |  1 | MATH  |  65 ||  2 | xiaohong |  41 |  4 |  4 | HISTORY |  30 ||  3 | xiaoxia |  22 |  3 |  3 | ENGLISH |  50 ||  4 | xiaogang |  32 |  1 |  1 | MATH  |  65 ||  5 | xiaoli  |  41 |  2 |  2 | CHINESE |  70 ||  6 | wangwu  |  13 |  2 |  2 | CHINESE |  70 ||  7 | lisi   |  22 |  3 |  3 | ENGLISH |  50 |+------+----------+------+------+------+---------+-------+7 rows in set (0.00 sec)

2.外连接

mysql> SELECT * FROM student LEFT JOIN class ON student.c_id = class.c_id;+------+----------+------+------+------+---------+-------+| s_id | s_name  | age | c_id | c_id | c_name | count |+------+----------+------+------+------+---------+-------+|  1 | xiaoming |  13 |  1 |  1 | MATH  |  65 ||  2 | xiaohong |  41 |  4 |  4 | HISTORY |  30 ||  3 | xiaoxia |  22 |  3 |  3 | ENGLISH |  50 ||  4 | xiaogang |  32 |  1 |  1 | MATH  |  65 ||  5 | xiaoli  |  41 |  2 |  2 | CHINESE |  70 ||  6 | wangwu  |  13 |  2 |  2 | CHINESE |  70 ||  7 | lisi   |  22 |  3 |  3 | ENGLISH |  50 ||  8 | zhangsan |  11 |  9 | NULL | NULL  | NULL |+------+----------+------+------+------+---------+-------+8 rows in set (0.00 sec)mysql> SELECT * FROM student RIGHT JOIN class ON student.c_id = class.c_id;+------+----------+------+------+------+---------+-------+| s_id | s_name  | age | c_id | c_id | c_name | count |+------+----------+------+------+------+---------+-------+|  1 | xiaoming |  13 |  1 |  1 | MATH  |  65 ||  4 | xiaogang |  32 |  1 |  1 | MATH  |  65 ||  5 | xiaoli  |  41 |  2 |  2 | CHINESE |  70 ||  6 | wangwu  |  13 |  2 |  2 | CHINESE |  70 ||  3 | xiaoxia |  22 |  3 |  3 | ENGLISH |  50 ||  7 | lisi   |  22 |  3 |  3 | ENGLISH |  50 ||  2 | xiaohong |  41 |  4 |  4 | HISTORY |  30 || NULL | NULL   | NULL | NULL |  5 | BIOLOGY |  40 |+------+----------+------+------+------+---------+-------+8 rows in set (0.00 sec)

总结

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