父表-sectionId是主键
| sectionId | Name |
| 1 | Section1 |
| 2 | Section2 |
| 3 | Section3 |
子表 - 复合键(sectionId 和 valueId)
| sectionId | valueId | LectureValue |
| 1 | 1 | somevalue1 |
| 1 | 2 | somevalue2 |
| 2 | 1 | somevalue3 |
| 2 | 2 | somevalue4 |
| 1 | 3 | somevalue5 |
| 2 | 3 | somevalue6 |
| 3 | 1 | somevalue7 |
| 3 | 2 | somevalue8 |
我希望根据sectionId填充valueId,例如
1-1
1-2
1-3
如果sectionId 2出现则
2-1
2-2
如果我第一次插入任何sectionId,相应的valueID应该为1,然后序列应该继续
有什么可能的方法可以在 MYSQL 本身中做到这一点吗?
最佳答案
不要存储像 2-1
这样的值。相反,当您需要这样的时候,请执行
SELECT CONCAT(sectionId, '-', valueId) AS my_fancy_valueId FROM table...
然后您可以通过使用 MyISAM 存储引擎的表来实现这一点。需要注意的是,它(尚)不支持外键或事务。
来自manual :
For MyISAM tables, you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as
MAX(auto_increment_column) + 1 WHERE prefix=given-prefix
. This is useful when you want to put data into ordered groups.
CREATE TABLE animals (
grp ENUM('fish','mammal','bird') NOT NULL,
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (grp,id)
) ENGINE=MyISAM;
INSERT INTO animals (grp,name) VALUES
('mammal','dog'),('mammal','cat'),
('bird','penguin'),('fish','lax'),('mammal','whale'),
('bird','ostrich');
SELECT * FROM animals ORDER BY grp,id;
Which returns:
+--------+----+---------+
| grp | id | name |
+--------+----+---------+
| fish | 1 | lax |
| mammal | 1 | dog |
| mammal | 2 | cat |
| mammal | 3 | whale |
| bird | 1 | penguin |
| bird | 2 | ostrich |
+--------+----+---------+
In this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values are reused if you delete the row with the biggest AUTO_INCREMENT value in any group. This happens even for MyISAM tables, for which AUTO_INCREMENT values normally are not reused.
关于mysql - 如何创建复合自动增量列,其中之一是分组方式,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30070903/