MYSQL Select from 2 tables with an id that is in just in one of them

Question

This is my question: I have 3 tables:

USERS

USERS_INFO

COMPANIES_INFO

The USERS table has a field ID The tables USERS_INFO and COMPANIES_INFO have a field ID_USER that is linked by a foreign key with ID .

The question is, how can I select a row that is present in just one of them?

An example:

USERS
+----+
| id |
+----+
| 1  | 
+----+
| 2  | 
+----+

USERS_INFO
+---------+---------+
| id_user | name    |
+---------+---------+
| 1       | Jhonny  |
+---------+---------+


COMPANIES_INFO
+---------+---------+
| id_user | company |
+---------+---------+
| 2       | Apple   |
+---------+---------+

What I want is something like this:

SELECT * FROM users_info, companies_info WHERE id_user=2

And get this:

id_user = 2
company = Apple

Instead if I did

SELECT * FROM users_info, companies_info WHERE id_user=1

I would have got:

id_user =1
name = Jhonny

I want for example select the user 2, by checking both tables USERS_INFO and COMPANIES_INFO because we don't know which one contains it... Any help?

Answer 1

Try this:

     SELECT U.id
     FROM users U
     LEFT JOIN users_info UI ON U.id = CI.id_user
     LEFT JOIN companies_info CI ON U.id = CI.id_user
     WHERE UI.id IS NOT NULL AND CI.id IS NOT NULL

Answer 2

You can try this:

SET @user = 1;
SELECT id_user, name FROM USERS_INFO WHERE id_user = @user
UNION
SELECT id_user, company as name FROM COMPANIES_INFO WHERE id_user = @user;