Question

I have this query select latitude, longitude, username, rank from users, but I only want that info if the username exist in my online_users db. That look like this:

id bigint(20)           
username varchar(16)
ip varchar(39)
time datetime

So if I have 3 users in my online_users db, I want the latitude, longitude, username and rank from my users table from those 3 users. How do I do this? I assume UNION something, but my sql skills are limited.

Answer 1

Assuming that these are two tables in the same database, and not two databases (as stated), then either of the following will work:

SELECT latitude, longitude, username, rank 
  FROM users INNER JOIN online_users ON users.username = online_users.username

SELECT latitude, longitude, username, rank 
  FROM users WHERE username IN (SELECT username FROM online_users)