Question

I have a table with a year and month in different columns, and I need to find all rows between 3 months ago and now.

SELECT * FROM `table` 
 WHERE DATE(CONCAT(`year`, '-', `month`, '-01')) >= 
          DATE_FORMAT(NOW() - INTERVAL 3 MONTH, '%Y-%m-01')

It just seems rather verbose, and possibly inefficient as this is a very large table. Is there a better way to do this?

Answer 1

There isn’t much optimization to be had when the date is stored as separate fields, but I would re-write your query as:

SELECT * 
  FROM `table` 
 WHERE STR_TO_DATE(`year`+ '-'+ `month` + '-01', '%Y-%m-%d') >= DATE_SUB(NOW(), INTERVAL 3 MONTH)

The concatenation renders indexing on the year and month columns useless.

For more info about MySQL date functions, see: http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html