title: SQL - Check if record exists in multiple tables
body: <p>I've been searching in stack for similiar questions but I couldn't find one that helps me with this issue, or I couldn't understand it.
  I've got 3 tables. </p>
  
  <pre><code>Users
  +---------+------+--------------+
  | id_user | name | age          |
  +---------+------+--------------+
  | user1   | John | 51           |
  +---------+------+--------------+
  | user2   | Jane | 65           |
  +---------+------+--------------+
  | user3   | Katie| 51           |
  +---------+------+--------------+
  | user4   | Marck| 65           |
  +---------+------+--------------+
  
  
  City1
  +---------+------+--------------+
  | id_user | time | street       |
  +---------+------+--------------+
  | user1   | 8    | 111111111111 |
  +---------+------+--------------+
  | user2   | 5    | 222222222222 |
  +---------+------+--------------+
  
  City2
  +---------+------+--------------+
  | user_id | time | street       |
  +---------+------+--------------+
  | user1   | 6    | 111111111111 |
  +---------+------+--------------+
  | user4   | 7    | 222222222222 |
  +---------+------+--------------+
  </code></pre>
  
  <p>I'm trying to do a query in order to know if a specific id_user exists in City1 and City2 tables. I don't really know how to strucuture it. For example, done id_user = user1, I would like to recieve something like city1 = true, city2=true. (in both tables, user1 exists); or done id_user=2, recieve city1=true, city2=false.</p>
  
  <p>Any ideas of how to do that?</p>