Error when adding foreign key

Question

I had a table named movies which had the fields id as primary key, and two varchars: title and genre.

I created a new table named genres with the int field id as primary key and desription varchar. I changed the field genre in my movies table so I could create a foreign key referencing a genre.

However, Mysql Workbench says there's an error when creating the foreign key.

Here's the statement:

ALTER TABLE `managemovies`.`movies` 
  ADD CONSTRAINT `genre_reference`
  FOREIGN KEY (`genre` )
  REFERENCES `managemovies`.`genres` (`id` )
  ON DELETE NO ACTION
  ON UPDATE NO ACTION
, ADD INDEX `genre_reference_idx` (`genero` ASC) ;

Error:

ERROR 1452: Cannot add or update a child row: a foreign key constraint fails  (`managemovies`.`#sql-3ba_2b`, CONSTRAINT `genre_reference` FOREIGN KEY (`genre`) REFERENCES `genres` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION)

SQL Statement: [... same statement than above ... ] ERROR: Error when running failback script. Details follow.

ERROR 1046: No database selected
SQL Statement:
CREATE TABLE `movies` [...]

[... the errors above repeated again ...]

Answer 1

clear your table contents and try adding foreign key.

if your table contain data which not matching the foreign key field value you will see this error ...

Answer 2

It looks like your table movies has data in genre column which is not present in genres.id column.

Your statement should work after removing the invalid data.

Hope it helps

Vishad

Answer 3

I have faced same issue i got resolved later..

for this answer is simple you just need to add atleast a row of values in both tables then try to add the foreign key