PL/PgSQL Dynamic Subqueries - sql

Question

I am creating a trigger that runs a check raises an exception if it passes. To do this I need to use a dynamic call because I only have the table name as a string. I am using PostgreSQL but I can't figure out how there execute command works. When I do this:
CREATE OR REPLACE FUNCTION bleep() RETURNS table(id INT) AS $bleep$
BEGIN
RETURN QUERY EXECUTE 'SELECT (id) from Applicant';
END;
$bleep$ LANGUAGE plpgsql;
SELECT * from bleep();
It works perfectly and I get back a table of id's from Applicant. But when I do this:
CREATE OR REPLACE FUNCTION bleep() RETURNS BOOLEAN AS $bleep$
BEGIN
IF (EXISTS (EXECUTE 'SELECT (id) from Applicant')) THEN
RETURN TRUE;
ELSE
RETURN FALSE;
END IF;
END;
$bleep$ LANGUAGE plpgsql;
It tells me:
ERROR: syntax error at or near "EXECUTE" Position: 87
This is just a toy example I made to figure out how this works and I have read lots of docs and guides. If I can figure out this toy example I can make the full trigger work since I tried it with hardcoding a table name. How can I make this work?

Answer 1

CREATE OR REPLACE FUNCTION bleep() RETURNS BOOLEAN AS $bleep$
DECLARE
res bool;
BEGIN
EXECUTE 'SELECT exists (select 1 from Applicant)' INTO res;
return res;
END;
$bleep$ LANGUAGE plpgsql;

Answer 2

CREATE OR REPLACE FUNCTION bleep() RETURNS BOOLEAN AS $bleep$
BEGIN
return query EXECUTE 'SELECT exists (select 1 from Applicant)';
END;
$bleep$ LANGUAGE plpgsql;

Answer 3

CREATE OR REPLACE FUNCTION bleep() RETURNS
BOOLEAN AS $bleep$
BEGIN
IF (EXISTS (SELECT id from Applicant)) THEN
RETURN TRUE;
ELSE
RETURN FALSE;
END IF;
END;
$bleep$ LANGUAGE plpgsql;

Answer 4

I misunderstood your question.
How about this?
CREATE FUNCTION bleep(integer) RETURNS boolean
AS 'select case when count(*) = 0 then false else true end from Applicant where id = $1;'
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;
You can test by SQLFiddle: http://sqlfiddle.com/#!15/33954/1