如何限制两个表之间一对多关系中的许多关系? [英] How to limit number of the many in a one-to-many relationships between two tables?

问题描述

我有一个带有两个MySql表的MySQL数据库.首先是与第一个表(表A)具有一列具有唯一值(从值(从1到n)的列.在第二个表2(表B)中，我有两列:在第一列中，我有一个名称，在第二个是从1到n的值(如果我在中添加一个值.第二个是表B中的已更新列，是对表A中第一个(反之亦然)的引用.

I have a MySQL database with two MySql tables. First is with The first table (table A) has a column with unique values(from values (from 1 to n). In the second table 2 (table B), I have two columns: in the first I have a name and in the second i have values from 1 to n(if i ad an value in the . The second it's updated column in table B is a reference to the first and vice versa. That's done)column in table A.

我的问题:我可以限制表A中第二个值出现在表B中的次数最多最多10次吗? 一个示例是这样的:(列val限制为3)(第三个表将发送错误)

My Question: Can I limit the number of aparation of times the values from the second in table A appear in table B, specifically to a maximum of 10 times? An example is this: (with limitation for column val to 3) (the third table would send an error)

First table:      Second table:        Third table(imaginary)
+---+             +----+-----+          +----+-----+ 
|val|             |name| val |          |name| val |
+---+             +----+-----+          +----+-----+
| 1 |             |  a |  1  |          |  a |  1  |          
| 2 |             |  b |  2  |          |  b |  2  |
+---+             |  c |  1  |          |  c |  1  |
                  |  d |  1  |          |  d |  1  |
                  +----+-----+          |  e |  1  |
                                        +----+-----+

PS:对不起，我的英语.

PS: Sorry for my english.

推荐答案

您需要在第二个表的表定义中添加约束.这样，数据库将在插入和更新时为您检查值.

You need to add a constraint to the table definition of the second table. This way, the database will check the value for you upon insert and update.

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