First learn about PostgreSQL stored procedures

CREATE OR REPLACE FUNCTION create_table_for_client(id int)

RETURNS integer AS

$BODY$

DECLARE

num int4 := 0;

sql "varchar";

BEGIN

sql := 'create table _' || id || '_company(id int, name text)';

EXECUTE sql;

sql := 'create table _' || id || '_employee(id int, name text)';EXECUTE sql;

sql := 'create table _' || id || '_sale_bill(id int, name text)';EXECUTE sql;

.......

return num;

END;

$BODY$ LANGUAGE plpgsql VOLATILE