SELECT * 
FROM TABLE_NAME
WHERE Date_Column >= DATEADD(MONTH, -3, GETDATE())

Mureinik's suggested method will return the same results, but doing it this way your query can benefit from any indexes on Date_Column .

or you can check against last 90 days.

SELECT * 
FROM TABLE_NAME
WHERE Date_Column >= DATEADD(DAY, -90, GETDATE())

Latest Versions of mysql don't support DATEADD instead use the syntax

DATE_ADD(date,INTERVAL expr type)

To get the last 3 months data use,

DATE_ADD(NOW(),INTERVAL -90 DAY) 
DATE_ADD(NOW(), INTERVAL -3 MONTH)

I'd use datediff , and not care about format conversions:

SELECT *
FROM   mytable
WHERE  DATEDIFF(MONTH, my_date_column, GETDATE()) <= 3

Last 3 months

SELECT DATEADD(dd,DATEDIFF(dd,0,DATEADD(mm,-3,GETDATE())),0)

Today

SELECT DATEADD(dd,DATEDIFF(dd,0,GETDATE()),0)

Last 3 months record

SELECT *, DATEDIFF(NOW(),`created_at`)as Datediff from `transactions` as t having Datediff <= 90