Question

In my jsp application I have a search box that lets user to search for user names in the database. I send an ajax call on each keystroke and fetch 5 random names starting with the entered string.
I am using the below query:
select userid,name,pic from tbl_mst_users where name like 'queryStr%' order by rand() limit 5
But this is very slow as I have more than 2000 records in my table.

Is there any better approach which takes less time and let me achieve the same..? I need random values.

Answer 1

How slow is “very slow”, in seconds?

The reason why your query could be slow is most likely that you didn’t place an index on name. 2000 rows should be a piece of cake for MySQL to handle.

The other possible reason is that you have many columns in the SELECT clause. I assume in this case the MySQL engine first copies all this data to a temp table before sorting this large result set.

I advise the following, so that you work only with indexes, for as long as possible:

SELECT userid, name, pic
FROM tbl_mst_users
JOIN (
    -- here, MySQL works on indexes only
    SELECT userid
    FROM tbl_mst_users
    WHERE name LIKE 'queryStr%'
    ORDER BY RAND() LIMIT 5
) AS sub USING(userid); -- join other columns only after picking the rows in the sub-query.

This method is a bit better, but still does not scale well. However, it should be sufficient for small tables (2000 rows is, indeed, small).

The link provided by @user1461434 is quite interesting. It describes a solution with almost constant performance. Only drawback is that it returns only one random row at a time.