MySQL query data table inside Time field is added today Count

One: So write post_category_id value can only be Chinese characters,, the number can not be found out, do not know why, the following statement to find out the count value is 0 because the value of post_category_id is a number

SELECT COUNT (*) from post WHERE post_category_id=18 and Date_format (created_on, '%y-%m-%d ') = Date_format (now (), '%y-%m-% d ')

Two: So write can get a total record number (post_category_id for data table one field)

SELECT COUNT (Date_format (created_on,'%y-%m-%d'as fromWHERE  post_ category_id=

MySQL query data table inside Time field is added today Count