Creo que el problema lo puedes tener en que el LEFT JOIN se esta haciendo entre
`AcaDB`.`cours_user` as `CU`y `No2008287`.`wrk_submission` AS `S` y
NO sobre (`AcaDB`.`user` as `U`, `AcaDB`.`cours_user` as `CU`) por eso da error la clausula ON ya que esta pertenece al LEFT JOIN. Deberias definir la relacion de `AcaDB`.`user` as `U` con las otras tablas.
Código:
FROM `AcaDB`.`user` as `U`,
`AcaDB`.`cours_user` as `CU`
LEFT JOIN `No2008287`.`wrk_submission` AS `S` ON `S`.`user_id` = `U`.`user_id`
AND ( `S`.`assignment_id` = 1 OR `S`.`assignment_id` IS NULL )
AND `S`.`original_id` IS NULL WHERE `U`.`user_id` = `CU`.`user_id`
AND `CU`.`code_cours` = '2008287'
intenta esto
....
Código:
....
FROM (`AcaDB`.`user` as `U`
JOIN `AcaDB`.`cours_user` as `CU`
ON `U`.`user_id` = `CU`.`user_id`)
LEFT JOIN `No2008287`.`wrk_submission` AS `S`
ON `S`.`user_id` = `U`.`user_id`
WHERE (`S`.`assignment_id` = 1
OR `S`.`assignment_id` IS NULL )
AND `S`.`original_id` IS NULL
AND `CU`.`code_cours` = '2008287'
tu sabras si debe ser JOIN o LEFT JOIN.
Quim