在Apache Derby数据库中声明外键 [英] Declaring foreign key in Apache Derby database

问题描述

我正在使用 ij 10.10的Apache Derby数据库.

I am using Apache Derby database with ij 10.10.

我有两个桌子.第一个是 usertable ，第二个是 logintable .在我的 usertable 中，有两列: userid 和 name .我的 logintable 表有两列: userid 和 password .我需要将 logintable 中的一列设置为外键，其中主键位于 usertable 中.

I have two tables. First is usertable and the second is logintable. In my usertable I have two columns: userid and name. My logintable table has two columns: userid and password. I need to set one column in logintable as foreign key where the primary key is in the usertable.

我使用以下命令创建表:

I used the following command to create the table:

create table usertable (userid varchar(10) primary key, name varchar(20));

如何编写 logintable 以将 userid 设置为引用上述主键的外键?

How do I write the logintable to set the userid as a foreign key referring to the above primary key?

有人可以帮我吗?

推荐答案

我认为您正在寻找FOREIGN KEY约束语法:

I think you're looking for the FOREIGN KEY constraint syntax: http://db.apache.org/derby/docs/10.10/ref/rrefsqlj13590.html

，更具体地说，是REFERENCES语法: http://db.apache.org/derby/docs/10.10/ref/rrefsqlj16357.html#rrefsqlj16357

And, more specifically, the REFERENCES syntax: http://db.apache.org/derby/docs/10.10/ref/rrefsqlj16357.html#rrefsqlj16357

因此，当您创建"logintable"时，在CREATE TABLE语句中的某个点上，您将具有以下内容:

So when you are creating the "logintable", at some point in the CREATE TABLE statement you will have something like:

 CONSTRAINT login_userid_ref FOREIGN KEY (userid) REFERENCES usertable(userid)

请注意，SQL语言具有各种备用语法样式，用于声明像这样的参照完整性约束.例如，您可以使用一种更简单的语法，最终得到如下结果:

Note that the SQL language has various alternate syntax styles for declaring referential integrity constraints like these; for example you can use a simpler syntax that ends up being something like:

create table logintable(
    userid varchar(10) references usertable(userid),
    password varchar(20));

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