Re: Advice on indexing a datetime column

[Jonathon Coombes]

Adding an index will add some overhead in terms of inserting/updating records. So if you are doing things like archiving or lots of updating, it may be a decrease in performance, depending on your application.

In terms of indexing the datetime column, this will offer benefit only if the queries are constructed to utilise that index. For example, if you are looking at getting data back for certain days, then this query may make lots of sense. However, if you are getting it over large amounts of time, or not time related, then MySQL may not even use the index.