sub queries question

[anishgiri]

I am trying to study sub queries, but correlated sub queries is not yet clear to me. Suppose I have users_tbl that have id and user_name column, I also have login_tbl that have id and last_login columns. How can I join the two table,getting the user_name and last_login using sub query? I know how to do this with join. Like this below

SELECT u.user_username, d.date_time_in
FROM users_tbl
JOIN last_login d ON u.user_id = d.user_id

But how to do this using sub query instead?