Mysql error 1452 - Cannot add or update a child row: a foreign key constraint fails

Question

I\'m having a bit of a strange problem. I\'m trying to add a foreign key to one table that references another, but it is failing for some reason. With my limited knowledge o

Answer 1

UPDATE sourcecodes_tags
SET sourcecode_id = NULL
WHERE sourcecode_id NOT IN (
  SELECT id FROM sourcecodes);

should help to get rid of those IDs. Or if null is not allowed in sourcecode_id, then remove those rows or add those missing values to the sourcecodes table.