PG::AmbiguousColumn: ERROR: ORDER BY "location" is ambiguous
LINE 5: ORDER BY location DESC, id
^

Simplified backtrace: async_exec -> block in execute_query -> log_connection_yield -> execute_query -> block in execute -> check_disconnect_errors -> execute -> _execute -> block (2 levels) in execute -> check_database_errors -> block in execute -> block in synchronize -> hold -> synchronize -> execute -> execute -> fetch_rows -> each -> to_a -> expected -> block (3 levels) in <top (required)> -> ------------------ -> --- Caused by: --- -> PG::AmbiguousColumn: -> ERROR: ORDER BY "location" is ambiguous -> LINE 5: ORDER BY location DESC, id -> ^ -> async_exec

$a1 = [2,2,3];
$a2 = [4,9,9];
$this->revTest(comp($a1, $a2), false);
Why?? Must be true

if the array is larger than another array, there will be an error, and you do not have a check

A problem with your code is not a kata issue.