Reports

Blacklisted phrase (0.5): Thanks
Long answer (-0.5):
Has code block (-0.5):
User mentioned (1): @progman
Self-answer (0.5):
Low reputation (0.5):

Actually I found a solution myself. It was sufficient to duplicate the constraint multiple times, each time with a different column:

  CONSTRAINT `RegistrationsInvoices1`
    FOREIGN KEY (`RegistrationID1`)
    REFERENCES `EBS`.`Registrations` (`RegistrationID`),
  CONSTRAINT `RegistrationsInvoices2`
    FOREIGN KEY (`RegistrationID2`)
    REFERENCES `EBS`.`Registrations` (`RegistrationID`),
  CONSTRAINT `RegistrationsInvoices3`
    FOREIGN KEY (`RegistrationID3`)
    REFERENCES `EBS`.`Registrations` (`RegistrationID`),
  CONSTRAINT `RegistrationsInvoices4`
    FOREIGN KEY (`RegistrationID4`)
    REFERENCES `EBS`.`Registrations` (`RegistrationID`),
  CONSTRAINT `RegistrationsInvoices5`
    FOREIGN KEY (`RegistrationID5`)
    REFERENCES `EBS`.`Registrations` (`RegistrationID`)

The only error was then just on the syntax of multiple constrains simultaneously. Thanks to @progman to pointing me in the right direction

79571533