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 is not special about SQL, it is about boolean logic. Your 1st statement is:

a AND b OR c

That means if any c is true, you get the row.

In a AND (b OR c)

you get only rows where a is true and (b or c) is true.