How to nest variable in query string passed to function - postgresql

Question

I need to be able to get the value stored inside rec_key.empname when I call this function:
CREATE OR REPLACE FUNCTION public.txt(text)
RETURNS SETOF record
LANGUAGE plpgsql
AS $function$
declare
var_param text;
var_req TEXT;
rec_key record;
cur_key CURSOR FOR Select empname::varchar from employee;
BEGIN
open cur_key;
loop
fetch cur_key into rec_key;
EXIT WHEN NOT FOUND;
var_req :=
'
' || $1 || '
';
return query execute var_req;
end loop;
close cur_key;
END
$function$
;
What do I have to change to get the desired empname when calling the function?
If I call it like this it doesn't work: :(
select * from public.txt('select empid, age::integer,''''''|rec_key.empname|''''''::varchar from employee') as (empid integer, age integer, empname varchar)

Answer 1

To address the question asked:
CREATE OR REPLACE FUNCTION public.txt(_sql text)
RETURNS SETOF record
LANGUAGE plpgsql AS
$func$
DECLARE
_rec record;
BEGIN
FOR _rec IN
SELECT empname::text FROM employee
LOOP
RETURN QUERY EXECUTE _sql
USING _rec.empname;
END LOOP;
END
$func$;
Call:
SELECT * FROM public.txt('SELECT empid, age::integer, $1 AS empname FROM employee')
AS (empid integer, age integer, empname varchar);
The example does not make any sense, though, and all of it could be replaced with a simple query. See my anser to your earlier question:
Doesn't find variable when passing query as parameter
Use the much simpler implicit cursor of a FOR loop. See:
Cursor based records in PostgreSQL
Truncating all tables in a Postgres database
Pass the variable as value with a USING clause. $1 is the symbol to reference the first USING argument. See:
Replace double quotes with single quotes in Postgres (plpgsql)