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

You are changing the condition when you are adding the parentheses.

In the initial case the result set consists of those records which satisfy the conditions

`date_next_payment` <= '2011-02-02' AND `status` = 'active' 

or the condition

 `status` = 'past due'.

After you add the parentheses the result set will consist of those records which satisfy the condition

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

and any of the conditions

`status` = 'active' 

or

`status` = 'past due'