Does adding 'LIMIT 1' to MySQL queries make them faster when you know there will only be 1 result?

Question

When I add LIMIT 1 to a MySQL query, does it stop the search after it finds 1 result (thus making it faster) or does it still fetch all of the results and truncate at the end?

Answer 1

If you really only expect one single result, it really makes sense to append the LIMIT to your query. I don't know the inner workings of MySQL, but I'm sure it won't gather a result set of 100'000+ records just to truncate it back to 1 at the end..

Answer 2

Depending on the query, adding a limit clause can have a huge effect on performance. If you want only one row (or know for a fact that only one row can satisfy the query), and are not sure about how the internal optimizer will execute it (for example, WHERE clause not hitting an index and so forth), then you should definitely add a LIMIT clause.

As for optimized queries (using indexes on small tables) it probably won't matter much in performance, but again - if you are only interested in one row than add a LIMIT clause regardless.

Answer 3

Limit can affect the performance of the query (see comments and the link below) and it also reduces the result set that is output by MySQL. For a query in which you expect a single result there is benefits.

Moreover, limiting the result set can in fact speed the total query time as transferring large result sets use memory and potentially create temporary tables on disk. I mention this as I recently saw a application that did not use limit kill a server due to huge result sets and with limit in place the resource utilization dropped tremendously.

Check this page for more specifics: MySQL Documentation: LIMIT Optimization

Answer 4

If there is only 1 result coming back, then no, LIMIT will not make it any faster. If there are a lot of results, and you only need the first result, and there is no GROUP or ORDER by statements then LIMIT will make it faster.