[英]MySql unique field by foreign key
Im Not sure if this question already been asked, because I think my question is not really clear... 林不知道是否已经问过这个问题,因为我认为我的问题还不清楚...
Let say i have this table : 假设我有这张桌子:
CREATE TABLE IF NOT EXISTS EntrepriseSpecialites
(
id_EntrepriseSpecialite INT AUTO_INCREMENT PRIMARY KEY
,id_Entreprise INT
,id_Specialite INT UNIQUE
);
At the moment, i can only have one id_Specialite with the same value in my table, but does there is a way to only an unique id_Specialite by id_Entreprise. 目前,我的表中只能有一个具有相同值的id_Specialite,但是有没有一种方法可以通过id_Entreprise只将一个唯一的id_Specialite。
Example : 范例:
id_EntrepriseSpecialite | id_Entreprise | id_Specialite
1 | 1 | 1
2 | 2 | 1
3 | 2 | 4
4 | 2 | 1 <- ops id_Entreprise 2 already have the id_Specialite 1
5 | 3 | 1
Why not make d_Entreprise
and id_Specialite
as your c ompound/composite Primary Key
, like: 为什么不将d_Entreprise
和id_Specialite
用作ompound/composite Primary Key
,例如:
CREATE TABLE IF NOT EXISTS EntrepriseSpecialites
(
id_Entreprise INT
,id_Specialite INT
, PRIMARY KEY (id_Entreprise, id_Specialite)
);
See SQLFiddle Demo 请参见SQLFiddle演示
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