oracle - Execute only one exists in SQL -

i'm creating report ireport on oracle db. have select values depending on condition this:

and exists (select 1 table_1 x = y)   or exists (select 1 table_2 z = y)  

is possible execute second exists if first false?

try use conditions in brackets:

and (         exists (select 1 table_1 x = y)        or exists (select 1 table_2 z = y)     )