ar_snippet_sql_4.sql

SELECT 
    `captains`.*
FROM
    `captains`
WHERE
    `captains`.`id` IN (SELECT 
            `boats`.`captain_id`
        FROM
            `boats`
        WHERE
            `boats`.`id` IN (SELECT 
                    `boat_classifications`.`boat_id`
                FROM
                    `boat_classifications`
                WHERE
                    `boat_classifications`.`classification_id` IN (SELECT 
                            `classifications`.`id`
                        FROM
                            `classifications`
                        WHERE
                            `classifications`.`name` = 'Sailboat')));