How exactly does using OR in a MySQL statement differ with/without parentheses?

Question

I have this query:

SELECT * FROM (`users`) WHERE `date_next_payment` <= \'2011-02-02\' 
    AND `status` = \'active\' OR `status` = \'past due\'
         


        

Answer 1

It's because when you are not using the parentheses you actually saying :

`date_next_payment` <= '2011-02-02'     AND `status` = 'active'
OR
`status` = 'past due'.

Which means that when status` = 'past due' this record would be shown too. regarless of passing the other conditions.

But when you do use parentheses you require:

 `date_next_payment` <= '2011-02-02'

AND to pass one of the two other conditions.