How does MySQL process ORDER BY and LIMIT in a query?

I have a query that looks like this: `SELECT article FROM table1 ORDER BY publish_date LIMIT 20` How does ORDER BY work? Will it order all records, then get the first 20, or will it get 20 records and order them by the `publish_date` field? If it's the last one, you're not guaranteed to really get the most recent 20 articles.