mysql time comparison returning zero records -

i have following query:

select * `appointment`  `appointment_full_date_from` = '2014-09-20 22:30:00'

and table appointment appointment

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the type of appointment_full_date_from , appointment_full_date_to datetime.

when run above query must return visible record table. not doing , returning 0 rows.

i tried following query no luck.

select * `appointment`  `appointment_full_date_from` = str_to_date('2014-09-20 22:30:00','%y-%m-%d %h:%i:%s')

what wrong here? can me?

UIO