CASE Statement between dates

Question

For my EntryDate column I've been trying to successfully separate my data by month and into specific names '2013_04','2013_05' etc, so I can later group my data by it also. This code has thus far been unsuccessful, how can it be changed to work?

CASE
WHEN EntryDate BETWEEN '2013-04-01' AND '2013-04-30' THEN '2013_04'
WHEN EntryDate BETWEEN '2013-05-01' AND '2013-05-31' THEN '2013_05'
WHEN EntryDate BETWEEN '2013-06-01' AND '2013-06-30' THEN '2013_06'
END

Thank you.

Answer 1

You can use DATE_FORMAT function:

DATE_FORMAT(EntryDate, '%Y_%m')

http://dev.mysql.com/doc/refman/5.6/en/date-and-time-functions.html#function_date-format

Answer 2

I would use the year() and month() functions, just because this is common across databases:

CONCAT_WS('_', YEAR(EntryDate), MONTH(EntryDate))

However, DATE_FORMAT() is also a good solution.

Answer 3

DATE_FORMAT（）是最佳选择，但是如果字符串函数和CONVERT可以使用不同的数字