Postgresql: fetch all not showing any data - postgresql

Question

Data is not showing when I tried to fetch data from cursor. dbo.show_cities_multiple2 is procedure which returns two cursors.
DO $$
<<first_block>>
DECLARE
counter refcursor := 0;
ca_cur refcursor:=null;
tx_cur refcursor:=null;
BEGIN
call dbo.show_cities_multiple2(ca_cur, tx_cur);
EXECUTE 'FETCH ALL from "' || tx_cur || '"';
RAISE NOTICE 'The current value of counter is %', ca_cur;
END first_block $$;

Answer 1

Your problem here is that you aren't actually doing anything with the results of your EXECUTE FETCH ... EXECUTE merely runs the statement that comes after it. A plpgsql function does not return anything unless you explicitly specify RETURN ...,RETURN NEXT ... or RETURN QUERY .... Furthermore, an anonymous DO $$ block cannot return any results. So if you want to actually retrieve rows from the cursor, you need to name your cursors and execute your fetch outside of the do block:
DO $$
<<first_block>>
DECLARE
counter integer := 0;
ca_cur refcursor:='ca_cur'; --name your cursors first, otherwise they will be anonymous!
tx_cur refcursor:='tx_cur';
BEGIN
call dbo.show_cities_multiple2(ca_cur, tx_cur);
...
END first_block $$;
--Fetch
FETCH ALL FROM tx_cur;
Alternatively, you can define a standard function and use RETURN NEXT OR RETURN QUERY to return the result sets from the cursors:
CREATE FUNCTION return_city_data() RETURNS SETOF cities AS $$
DECLARE
counter integer = 0;
tx_cur refcursor = 'tx_cur';
ca_cur refcursor = 'ca_cur';
rec RECORD;
BEGIN
CALL dbo.show_cities_multiple(tx_cur,ca_cur);
-- Iterate over each record in the cursor
FOR rec in EXECUTE 'FETCH ALL FROM ' || tx_cur LOOP
counter = counter + 1;
-- RETURN NEXT means "Append each value to the function's result set".
RETURN NEXT rec;
END LOOP;
FOR rec in EXECUTE 'FETCH ALL FROM ' || ca_cur LOOP
counter = counter + 1;
RETURN NEXT rec;
END LOOP;
--All records have been appended to the result set. the cursors can now be closed.
CLOSE tx_cur;
CLOSE ca_cur;
RAISE NOTICE 'The current value of counter is %', "counter";
END
$$ LANGUAGE plpgsql;
OR
CREATE FUNCTION return_city_data() RETURNS SETOF cities AS $$
DECLARE
counter integer = 0;
tx_cur refcursor = 'tx_cur';
ca_cur refcursor = 'ca_cur';
rec RECORD;
BEGIN
CALL dbo.show_cities_multiple(tx_cur,ca_cur);
-- RETURN QUERY means "append all rows from the query to the function's result set"
RETURN QUERY EXECUTE 'FETCH ALL FROM ' || tx_cur;
RETURN QUERY EXECUTE 'FETCH ALL FROM ' || ca_cur;
CLOSE tx_cur;
CLOSE ca_cur;
END
$$ LANGUAGE plpgsql;
You can use either of these forms with a simple SELECT statement:
SELECT * FROM return_city_data();
Note that unlike RETURN, RETURN NEXT and RETURN QUERY do not terminate your function and you can use them multiple times in your blocks. The function will then naturally terminate at the end of the last block.