MySQL 外键约束：更新一个表时，用第一个表中的一些数据填充另一个表

Question

I have two tables, users table and login table. Say:

Create table users(
 id int not null,
 name varchar not null,
 email varchar not null,
 password varchar not null,
 entries int default 0,
 primary key(id));

Create table login(
 id int not null,
 email varchar not null,
 password varchar not null,
 user_id int not null,
 Primary key(id)),
 Foreign key (user_id) references users(id));

What constraints can I add or how can i work my way around such that whenever i add a user in the users table, the email and password columns are added into the login table too (just like to say i create a minimized version of the users table which only contains login credentials of users) . And whenever i delete a user from the users table, he should be removed from the login table.

I hope i have been descriptive enough

Answer 1

You can define constraint with cascade delete . To implement the update of dependent tables you need triggers . It is possible to define AFTER INSERT trigger where you can update any dependent tables.

At the same time, I would reconsider having redundant fields in the dependent table when you always can obtain it by joining with the main table.