Search notes:

SQL precedence (AND, OR)

In most RDMBS (all?), and has a higher precedence than or when used in a where clause.

Because of this precedence rule, and conditions are evaluated before or conditions.

where condition is true:

select count(*) from …
where
   1 = 1            or
   1 = 2 and 1 = 3
;

where condition is false

select count(*) from …
where
   1 = 0            or
   1 = 1 and 1 = 3
;