sql - Mysql DateTime group by 15 mins

Question

I have a table that looks like this

CREATE TABLE `time_table` (
 `id` INT(10) NOT NULL AUTO_INCREMENT,
 `creationDate` DATETIME NOT NULL,
 PRIMARY KEY (`id`)
)

I basically store the creation time of certain records in the table. I know if I want to get a count of the records that were created in 15 mins interval I will use something like this

SELECT FLOOR(UNIX_TIMESTAMP(creationDate)/900) AS t, 
COUNT(*) FROM time_table
GROUP BY t

That gives me something like this

t          COUNT(*)
1434187    1
1434188    3
1434189    2
1434190    2

How do I make sense of the first column? If I want it to show me something like

t                 COUNT(*)
2:00pm - 2:15pm   1
2:15pm - 2:30pm   3
2:30pm - 2:45pm   2
2:45pm - 3:00pm   2

I understand that with some manipulation I could get 1434187 to show up at 2:15pm. Even that might be a good start....then with some logic I could show the entire period. Thanks!

Answer 1

Here is the solution I use:

SELECT  FROM_UNIXTIME(FLOOR( UNIX_TIMESTAMP(creationDate)/900 ) * 900) AS t, COUNT(*) FROM time_table GROUP BY t

Although it arrives 4 years later, hope it will be useful to someone.