Datetime vs Date and Time Mysql

Question

I generally use datetime field to store created_time updated time of data within an application.

But now i have come across a database table where they have kept dat

Answer 1

There is a huge difference in performance when using DATE field above DATETIME field. I have a table with more then 4.000.000 records and for testing purposes I added 2 fields with both their own index. One using DATETIME and the other field using DATE.

I disabled MySQL query cache to be able to test properly and looped over the same query for 1000x:

SELECT * FROM `logs` WHERE `dt` BETWEEN '2015-04-01' AND '2015-05-01' LIMIT 10000,10; DATETIME INDEX: 197.564 seconds.

SELECT * FROM `logs` WHERE `d` BETWEEN '2015-04-01' AND '2015-05-01' LIMIT 10000,10; DATE INDEX: 107.577 seconds.

Using a date indexed field has a performance improvement of: 45.55%!!

So I would say if you are expecting a lot of data in your table please consider in separating the date from the time with their own index.