// Associative array: single record
$record = [ 'thread_id' => 'adasdasdasd', 'message_id' => 'rwerwer32234' ];
$record = [ 'thread_id' => '56h34r', 'message_id' => '344536sdf' ];

// Numerically indexed array: multiple records
$records = [ $record1, $record2 ];