Plpgsql; store all table names into an array - sql

Question

My main purpose is actually, filtering all table names contain 'Messdaten' in it (for example "ID: 843063334 CH: 0001 Messdaten") and create new tables out of them with 'create table as' command as 'Backup_Messdaten1', 'Backup_Messdaten2', etc.
First I was trying to store all table names without filtering (there is maybe a way to retrieve all table names, contain 'Messdaten' in it by sql query, I don't know), and then storing the ones contain 'Messdaten' into another array and using that new array in the 'create table as' command.
But as I said my first goal is just to store all table names into an array;
Code itself;
CREATE OR REPLACE FUNCTION retrieve()
RETURNS text[] AS
$BODY$DECLARE
tbl_names text[];
BEGIN
tbl_names := array(SELECT table_name FROM information_schema.tables WHERE
table_schema='public' AND table_type='BASE TABLE');
SELECT tbl_names[i] FROM generate_subscripts(tbl_names, 1) g(i);
END;$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION retrieve()
OWNER TO postgres;
But for the code above, I am getting such an error;
Error;
ERROR: could not find array type for data type information_schema.sql_identifier
SQL state: 42704
Context: SQL statement "SELECT array(SELECT table_name FROM information_schema.tables WHERE table_schema='public' AND table_type='BASE TABLE')"
PL/pgSQL function retrieve() line 4 at assignment
Do you have any idea what is wrong with it and by the way I explained my main purpose, I would appreciate it If you point me to the right direction regarding that purpose.

Answer 1

SELECT array_agg(table_name::text)
FROM information_schema.tables
WHERE table_schema='public' AND table_type='BASE TABLE';
You need to cast the table name to text. The subquery is unnecessary, and you need to use array_agg not the array pseudo-function.
Personally I don't see why you need to aggregate them into an array at all, though. I'd just:
DECLARE
tablename text;
BEGIN
FOR tablename IN
SELECT table_name FROM information_schema.tables
WHERE table_schema='public' AND table_type='BASE TABLE'
AND ... my extra filters here ...
LOOP
EXECUTE format('CREATE TABLE %I AS TABLE %I', tablename || '_backup', tablename);
END LOOP;
END;

Answer 2

Your code contains more errors - basic error is missing any RETURN statement (for PL/pgSQL language). You can use SQL language too (see my example)
Postgres doesn't support arrays for some types - sql_identifier is one. You can try to use a casting to some basic type - in this case to text.
CREATE OR REPLACE FUNCTION names(filter text)
RETURNS text[] AS $$
SELECT array_agg(table_name::text)
FROM information_schema.tables
WHERE table_schema='public'
AND table_type='BASE TABLE' AND table_name LIKE $1;
$$ LANGUAGE sql;
postgres=# select names('foo%');
names
------------
{foo1,foo}
(1 row)