Why doesn't query with subquery work in mysql 5.7?

Question

MySQL

Unable to execute such query in mysql 5.7

SELECT
  routes.id_zadakur taskId,
  sum(BS_TIME_DIFF(routes.arrival,routes.departure)) wait,
  sum(BS_TIME_DIFF((SELECT r2.departure FROM routes r2 WHERE routes.series = r2.series + 1 AND r2.id_zadakur = taskId),routes.arrival)) active
FROM routes
GROUP BY routes.id_zadakur

gives such an error

[42S22][1054] Unknown column 'taskId' in 'where clause'

At the same time, in mysql5.5, queries are executed perfectly. What is the difference, how can the query be rewritten to work on 5.7 as well?

Answer 1

SELECT
    r.id_zadakur taskId,
    sum(BS_TIME_DIFF(r.arrival, r.departure)) wait,
    sum(BS_TIME_DIFF((
        SELECT r2.departure FROM routes r2 
        WHERE r.series = r2.series + 1 AND r2.id_zadakur = r.id_zadakur
    ), r.arrival)) active
FROM routes r
GROUP BY routes.id_zadakur

Answer 2

SELECT `r`.`id_zadakur` AS `taskId`,
       sum(BS_TIME_DIFF(`r`.`arrival`, `r`.`departure`)) AS `wait`,
       sum(BS_TIME_DIFF(IFNULL(`r2`.`departure`, `r`.`arrival`), `r`.`arrival`)) AS `active`
  FROM `routes` AS `r`
  LEFT JOIN `routes` AS `r2` ON `r2`.`id_zadakur` = `r`.`id_zadakur` AND `r2`.`series` = `r`.`series`-1 
  GROUP BY `r`.`id_zadakur`