MySQL select rows that do not have matching column in other table

Question

I can\'t seem to figure this out so far. I am trying to join two tables and only select the rows in table A that do not have a matching column in table B. For example, lets

Answer 1

Try this SQL:

SELECT users.username
FROM  users
LEFT JOIN sent ON sent.username = users.username
WHERE sent.username IS NULL;

The better way in my opinion would be:

SELECT users.username
FROM  users
LEFT JOIN sent ON sent.id = users.id
WHERE sent.id IS NULL;

As both the id fields, would be indexed (primary key I would have thought) so this query would be better optimised than the first one I suggested.

However you may find my first suggestion better for you, it depends on what your requirements are for your application.