Array error passing dynamic number of parameters to function - postgresql

Question

I'm trying to create a function to receive the name of the table in my schema already created and a several name of columns within this table (dynamic number of columns) and return a table with all the columns in a unique column with the value of each column separated by comma.
I'm trying this:
CREATE OR REPLACE PROCEDURE public.matching(IN table text, VARIADIC column_names text[])
LANGUAGE 'plpgsql'
AS $BODY$DECLARE
column_text text;
BEGIN
EXECUTE format ($$ SELECT array_to_string(%s, ' ')$$, column_names) into column_text;
EXECUTE format ($$ CREATE TABLE temp1 AS
SELECT concat(%s, ' ') FROM %s $$, column_text, table);
END;$BODY$;
This return an error:
ERROR: syntax error at or near «{»
LINE 1: SELECT array_to_string({city,address}, ' ')
which is the error?

Answer 1

If you simplify the generation of the dynamic SQL, things get easier:
CREATE OR REPLACE PROCEDURE public.matching(IN table_name text, VARIADIC column_names text[])
LANGUAGE plpgsql
AS
$BODY$
DECLARE
l_sql text;
BEGIN
l_sql := format($s$
create table temp1 as
select concat_ws(',', %s) as everything
from %I
$s$, array_to_string(column_names, ','), table_name);
raise notice 'Running %', l_sql;
EXECUTE l_sql;
END;
$BODY$;
So if you e.g. pass in 'some_table' and {'one', 'two', 'three'} the generated SQL will look like this:
create table temp1 as select concat_ws(',', one,two,three) as everything from some_table
I also used a column alias for the new column, so that the new table has a defined name. Note that the way I put the column names into the SQL string won't properly deal with identifiers that need double quotes (but they should be avoided anyway)
If you want to "return a table", then maybe a function might be the better solution:
CREATE OR REPLACE function matching(IN table_name text, VARIADIC column_names text[])
returns table (everything text)
LANGUAGE plpgsql
AS
$BODY$
DECLARE
l_sql text;
BEGIN
l_sql := format($s$
select concat_ws(',', %s) as everything
from %I
$s$, array_to_string(column_names, ','), table_name);
return query execute l_sql;
END;
$BODY$;
Then you can use it like this:
select *
from matching('some_table', 'one', 'two', 'three');

Answer 2

I propose different but similar code.
With following script:
CREATE OR REPLACE PROCEDURE public.test(IN p_old_table text, IN p_old_column_names text[], IN p_new_table text)
LANGUAGE 'plpgsql'
AS $BODY$
DECLARE
old_column_list text;
ctas_stmt text;
BEGIN
old_column_list = array_to_string(p_old_column_names,',');
RAISE NOTICE 'old_column_list=%', old_column_list;
ctas_stmt = format('CREATE TABLE %s AS SELECT %s from %s', p_new_table, old_column_list, p_old_table);
RAISE NOTICE 'ctas_stmt=%', ctas_stmt;
EXECUTE ctas_stmt;
END;
$BODY$;
--
create table t(x int, y text, z timestamp, z1 text);
insert into t values (1, 'OK', current_timestamp, null);
select * from t;
--
call test('t',ARRAY['x','y','z'], 'tmp');
--
\d tmp;
select * from tmp;
I have following execution:
CREATE OR REPLACE PROCEDURE public.test(IN p_old_table text, IN p_old_column_names text[], IN p_new_table text)
LANGUAGE 'plpgsql'
AS $BODY$
DECLARE
old_column_list text;
ctas_stmt text;
BEGIN
old_column_list = array_to_string(p_old_column_names,',');
RAISE NOTICE 'old_column_list=%', old_column_list;
ctas_stmt = format('CREATE TABLE %s AS SELECT %s from %s', p_new_table, old_column_list, p_old_table);
RAISE NOTICE 'ctas_stmt=%', ctas_stmt;
EXECUTE ctas_stmt;
END;
$BODY$;
CREATE PROCEDURE
create table t(x int, y text, z timestamp, z1 text);
CREATE TABLE
insert into t values (1, 'OK', current_timestamp, null);
INSERT 0 1
select * from t;
x | y | z | z1
---+----+----------------------------+----
1 | OK | 2020-04-14 11:37:28.641328 |
(1 row)
call test('t',ARRAY['x','y','z'], 'tmp');
psql:tvar.sql:24: NOTICE: old_column_list=x,y,z
psql:tvar.sql:24: NOTICE: ctas_stmt=CREATE TABLE tmp AS SELECT x,y,z from t
CALL
Table "public.tmp"
Column | Type | Collation | Nullable | Default
--------+-----------------------------+-----------+----------+---------
x | integer | | |
y | text | | |
z | timestamp without time zone | | |
select * from tmp;
x | y | z
---+----+----------------------------
1 | OK | 2020-04-14 11:37:28.641328
(1 row)