Compound FULLTEXT index in MySQL

Question

I would like to make system whitch allows to search user messages, by specific user. assume having folowing table

create table messages(
  user_id int,
  mes         


        

Answer 1

You should add a fulltext index on message and a regular index on user_id, and use the query:

SELECT *
FROM messages
WHERE MATCH(message) AGAINST(@search_query)
AND user_id = @user_id;

You're right that you can't do option 3. But rather than trying to pick between 1 and 2, let MySQL do the work for you. MySQL will only use one of the two indexes, and will do a linear scan to complete the second filter, but it will estimate the effectiveness of each index and choose the optimal one.

Note: only do this if you can afford the overhead of two indexes (slower insert/update/delete). Also, if you know that each user will only have a few messages, then yes it might make sense to use a simple index and do a regex in the application layer or something like that.