Question

I’m new in sql. I have doubt. Let’s say that I have two tables. One is called user and the other order.

User
User_Id - name - email

Order
Order_id - product - User_id

What query should I use to insert a new order in the order table with the User_id field related to the User_id from the user table(an existing user)

Eg:

Order_id - product - User_id
1a - plate - 1
2a - car - 3
3a - bike - 1

Answer 1

If you have name or email of the user, you can try this. If USER has a composite primary key on user_id and name columns, it will work without any issues. Better to keep foreign key relationship on user_id column of ORDER also.

Example has NAME column, you can try with email column also.

INSERT INTO ORDER (ORDER_ID, PRODUCT, USER_ID)
VALUES (1a, 'plate', (SELECT USER_ID FROM USER WHERE NAME = 'Existing user'));

EDIT:

I have worked on Oracle sql only. After your comment, found this link.

http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html

If you have defined AUTO_INCREMENT on order_id column, you don’t need to pass value.

INSERT INTO ORDER (PRODUCT, USER_ID)
VALUES ('plate', (SELECT USER_ID FROM USER WHERE NAME = 'Existing user'));