PostgreSQL: Iterating over array of text and executing SQL - postgresql

Question

I am copying tables from one schema to another. I am trying to pass argument of name of tables that I want to copy. But no table is created in Schema when I execute the CALL.
Command: CALL copy_table('firstname', 'tableName1,tableName2,tableName3');
CREATE OR REPLACE PROCEDURE copy_table(user VARCHAR(50), strs TEXT)
LANGUAGE PLPGSQL
AS $$
DECLARE
my_array TEXT;
BEGIN
FOR my_array IN
SELECT string_to_array(strs, ',')
LOOP
EXECUTE 'CREATE TABLE ' || user || '.' || my_array || ' (LIKE public.' || my_array || ' INCLUDING ALL)';
END LOOP;
$$
Could you please help? Thank you.

Answer 1

The function string_to_array returns an array value. Looping through arrays is performed by FOREACH command, not FOR.
See documentation:
https://www.postgresql.org/docs/14/plpgsql-control-structures.html#PLPGSQL-FOREACH-ARRAY
CREATE FUNCTION sum(int[]) RETURNS int8 AS $$
DECLARE
s int8 := 0;
x int;
BEGIN
FOREACH x IN ARRAY $1
LOOP
s := s + x;
END LOOP;
RETURN s;
END;
$$ LANGUAGE plpgsql;

Answer 2

Loop over an array with FOREACH like Simon suggested. Or with FOR in old (or any) versions. See:
Iterating over integer[] in PL/pgSQL
Typically, a set-based solution is shorter and faster, though:
CREATE OR REPLACE PROCEDURE copy_tables(_schema text, VARIADIC _tables text[])
LANGUAGE plpgsql AS
$proc$
BEGIN
EXECUTE
(SELECT string_agg(format('CREATE TABLE %1$I.%2$I (LIKE public.%2$I INCLUDING ALL)', _schema, t), E';\n')
FROM unnest(_tables) t);
END
$proc$;
About VARIADIC:
Return rows matching elements of input array in plpgsql function
Call, passing list of table names:
CALL copy_tables('firstname', 'tableName1', 'tableName2', 'tableName3');
Or, passing genuine array:
CALL copy_tables('foo', VARIADIC '{tableName1,tableName2,tableName3}');
Or, passing (and converting) comma-separated string (your original input):
CALL copy_tables('foo', VARIADIC string_to_array('tableName1,tableName2,tableName3', ','));
I use format() to concatenate the SQL string safely. Note that identifiers must be passed as case-sensitive strings! See:
Define table and column names as arguments in a plpgsql function?
SQL injection in Postgres functions vs prepared queries