sqlconcat two variables postgresql - sql

Question

Im writing a psql function. I want to do a concat between two variables inside psql.
and im getting syntax_error.
Let's notice that date_contract is of type date.
Thank you Who can help me
declare
result_table regclass := $$public.contract$$||text;
time_now time
BEGIN
execute $$SELECT MIN(date_contract) FROM $$||result_table INTO date_;
execute $$SELECT CURRENT_TIMESTAMP::time FROM $$||result_table INTO time_now;
execute $$
INSERT INTO $$||result_table||$$
(id, dat_beg_contract, dat_end_contract,date_contract, long_c)
SELECT id, dat_beg_contract, dat_end_contract, sum(extract(epoch from (least(s.dat_beg_contract, gs.date_contract||time_ + interval '1 day')::timestamp -
greatest(s.dat_beg_contract, gs.date_contract)
)
) / 60) as long_c
$$;
END;

Answer 1

This code block might give you an idea of how to concatenate variables
DO $$
DECLARE
rec1 text;rec2 text;
BEGIN
EXECUTE 'SELECT ''foo'' ' INTO rec1;
EXECUTE 'SELECT ''bar'' 'INTO rec2;
RAISE NOTICE 'Option 1 %, Opiton 2: %', rec1||rec2, rec1||' '||rec2 ;
END; $$ LANGUAGE plpgsql;
NOTICE: Option 1 foobar, Opiton 2: foo bar
EDIT Returning a query with a function
CREATE TABLE tab (id int);
INSERT INTO tab VALUES (100),(42);
CREATE OR REPLACE FUNCTION myfunc (table_name TEXT)
RETURNS TABLE (res int) AS $$
DECLARE v1 int; v2 int;
BEGIN
EXECUTE 'SELECT max(id) FROM '||table_name INTO v1;
EXECUTE 'SELECT min(id) FROM '||table_name INTO v2;
RETURN QUERY EXECUTE 'SELECT ' || v1 || v2 ;
END;
$$ LANGUAGE plpgsql;
SELECT myfunc('tab');
myfunc
--------
10042
EDIT 2 Example concatenating timestamp and integer
CREATE TABLE tab (id int);
INSERT INTO tab VALUES (100),(42);
CREATE OR REPLACE FUNCTION myfunc (table_name TEXT)
RETURNS TABLE (res text) AS $$
DECLARE v1 int; v2 timestamp;
BEGIN
EXECUTE 'SELECT min(id) FROM '||table_name INTO v1;
EXECUTE 'SELECT CURRENT_TIMESTAMP' INTO v2;
RETURN QUERY EXECUTE 'SELECT ' || quote_literal(v1 || ' - ' ||v2) ;
END;
$$ LANGUAGE plpgsql;
SELECT myfunc('tab');
EXECUTE 'SELECT min(id) FROM '||table_name INTO v1;
EXECUTE 'SELECT CURRENT_TIMESTAMP' INTO v2;
RETURN QUERY EXECUTE 'SELECT ' || quote_literal(v1::text || ' - ' ||v2) ;
END;
$$ LANGUAGE plpgsql;
SELECT myfunc('tab');
myfunc
--------------------------------
42 - 2021-02-02 15:54:24.24179
(1 Zeile)
EDIT 3 let me know if this works, so that I can clean the answer
CREATE TABLE tab (date_contract date);
INSERT INTO tab VALUES (current_date+7),(current_date);
CREATE OR REPLACE FUNCTION myfunc (table_name TEXT)
RETURNS TABLE (date_contract date, col_new text) AS $$
DECLARE date_ date;
BEGIN
EXECUTE 'SELECT min(date_contract) FROM '||table_name INTO date_;
RETURN QUERY EXECUTE 'SELECT date_contract,'|| quote_literal(date_|| ' ' ||current_time) ||' FROM ' || table_name;
END;
$$ LANGUAGE plpgsql;
SELECT * FROM myfunc('tab');
date_contract | col_new
---------------+-------------------------------
2021-02-09 | 2021-02-02 16:29:49.013344+01
2021-02-02 | 2021-02-02 16:29:49.013344+01
(2 Zeilen)