[Python知识库]Python django之基于双下划线的跨表查询：一对多

1 mysql JOIN 查询

使用join查询金瓶梅这本书出版社的名字

MariaDB [orm]> select * from book;
+-----+------------+-------------+--------+------------+
| nid | title      | publishDate | price  | publish_id |
+-----+------------+-------------+--------+------------+
|   1 | 红楼梦     | 2001-04-01  | 200.00 |          1 |
|   2 | 西游记     | 2001-04-01  | 200.00 |          1 |
|   3 | 水浒传     | 2001-04-01  | 200.00 |          1 |
|   4 | 红楼梦     | 2001-04-01  | 200.00 |          1 |
|   5 | 西游记     | 2001-04-01  | 200.00 |          1 |
|   6 | 水浒传     | 2001-04-01  | 200.00 |          1 |
|   7 | 金瓶梅     | 2001-04-01  | 200.00 |          1 |
|   8 | 金瓶梅1    | 2001-04-01  | 200.00 |          1 |
|   9 | 金瓶梅2    | 2001-04-01  | 200.00 |          1 |
|  10 | 金瓶梅3    | 2001-04-01  | 200.00 |          1 |
|  11 | 金瓶梅3    | 2001-04-01  | 200.00 |          1 |
+-----+------------+-------------+--------+------------+
11 rows in set (0.001 sec)

MariaDB [orm]> select * from publish;
+-----+-----------------+--------+---------------------+
| nid | name            | city   | email               |
+-----+-----------------+--------+---------------------+
|   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   2 | 河北出版社      | 河北   | wangze@163.com      |
|   3 | 人民出版社      | 北京   | 15532634791@163.com |
|   4 | 河北出版社      | 河北   | wangze@163.com      |
+-----+-----------------+--------+---------------------+
4 rows in set (0.001 sec)

MariaDB [orm]> select * from book inner join publish on book.publish_id = publish.nid;
+-----+------------+-------------+--------+------------+-----+-----------------+--------+---------------------+
| nid | title      | publishDate | price  | publish_id | nid | name            | city   | email               |
+-----+------------+-------------+--------+------------+-----+-----------------+--------+---------------------+
|   1 | 红楼梦     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   2 | 西游记     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   3 | 水浒传     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   4 | 红楼梦     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   5 | 西游记     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   6 | 水浒传     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   7 | 金瓶梅     | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   8 | 金瓶梅1    | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|   9 | 金瓶梅2    | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|  10 | 金瓶梅3    | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
|  11 | 金瓶梅3    | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
+-----+------------+-------------+--------+------------+-----+-----------------+--------+---------------------+
11 rows in set (0.001 sec)

MariaDB [orm]> select * from book inner join publish on book.publish_id = publish.nid where book.title='金瓶梅';
+-----+-----------+-------------+--------+------------+-----+-----------------+--------+---------------------+
| nid | title     | publishDate | price  | publish_id | nid | name            | city   | email               |
+-----+-----------+-------------+--------+------------+-----+-----------------+--------+---------------------+
|   7 | 金瓶梅    | 2001-04-01  | 200.00 |          1 |   1 | 人民出版社      | 北京   | 15532634791@163.com |
+-----+-----------+-------------+--------+------------+-----+-----------------+--------+---------------------+
1 row in set (0.001 sec)

MariaDB [orm]> select publish.name from book inner join publish on book.publish_id = publish.nid where book.title='金瓶梅';
+-----------------+
| name            |
+-----------------+
| 人民出版社      |
+-----------------+
1 row in set (0.001 sec)