How to compare the results of two queries?

I am developing a task in which I need to know how to compare the
results of two queries ...
I thought about creating a procedure which both queries received by
parameters respectively. Then somehow able to run queries and return if
both have the same result. As a feature of the problem, both queries are
selection.
Here I leave a piece of code I want to do.

create or replace function compare(sql1 character varying, sql2
character varying) returns boolean as
$body$
Declare
Begin
--here in some way to run both queries and then compare
End;
$body$
language 'plpgsql';

I've been studying and I found that there EXECUTE but to use it, first
you should have used PREPARE, and in this case the values ​​of the
parameters are already made ​​inquiries.
For example the execution of the function would be something like ...

select compare('select * from table1', 'select * from table2');

For this case the result is false, then the queries are executed on
different tables.
Thanks in advance.
Best regards from Cuba.
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