Question

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Error appears in sql when trying to add multiple foreign keys

I am trying to alter a table so That I can add a foreign key constraint in mysql database:

ALTER TABLE  `Question` ADD CONSTRAINT `FK_question` FOREIGN KEY (`QuestionId`)
REFERENCES `Image_Question` (`QuestionId`) ON DELETE CASCADE ;

Problem is that it is giving me this error:

1452 – Cannot add or update a child row: a foreign key constraint fails (mobile_app.

‘#sql-4517_15241’>, CONSTRAINT FK_question FOREIGN KEY
(QuestionId) REFERENCES Image_Question (QuestionId) ON DELETE
CASCADE)

What does this error actually mean and what are the possible solutions I might have to undertake in order to fix this?

Answer 1

Probably Image_Question.QuestionId is not unique. And it also looks like the FK should go the other way around, from Image_Question to Question