数据库-mysql数据连接

a; +------+ | name | +------+ | 1 | | 2 | | 3 | | 4 | +------+ 4 rows in set (0.00 sec) MariaDB [test2]> select * from b; +------+ | name | +------+ | 3 | | 4 | | 5 | | 6 | +------+ 4 rows in set (0.00 sec) MariaDB [test2]> select * from a inner join b on a.name=b.name; +------+------+ | name | name | +------+------+ | 3 | 3 | | 4 | 4 | +------+------+ 2 rows in set (0.00 sec) MariaDB [test2]> select * from a,b where a.name=b.name; +------+------+ | name | name | +------+------+ | 3 | 3 | | 4 | 4 | +------+------+ 2 rows in set (0.00 sec)

三：LEFT JOIN

MySQL left join 与 join 有所不同。 MySQL LEFT JOIN 会读取左边数据表的全部数据，即便右边表无对应数据。

MariaDB [test2]> select * from a left join b on a.name=b.name;
+------+------+
| name | name |
+------+------+
|    3 |    3 |
|    4 |    4 |
|    1 | NULL |
|    2 | NULL |
+------+------+
4 rows in set (0.00 sec)

四： RIGHT JOIN

MySQL RIGHT JOIN 会读取右边数据表的全部数据，即便左边边表无对应数据。

MariaDB [test2]> select * from a right join b on a.name=b.name;
+------+------+
| name | name |
+------+------+
|    3 |    3 |
|    4 |    4 |
| NULL |    5 |
| NULL |    6 |
+------+------+
4 rows in set (0.00 sec)

 

五：full join 

　　两个表的并集

　　

MariaDB [test2]> select * from a left join b on a.name =b.name union select * from a right join b on a.name =b.name;
+------+------+
| name | name |
+------+------+
|    3 |    3 |
|    4 |    4 |
|    1 | NULL |
|    2 | NULL |
| NULL |    5 |
| NULL |    6 |
+------+------+
6 rows in set (0.00 sec)

 

数据库-mysql数据连接

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