Question

I was dumb and created a year ago tables for a customer. Now I know better and should have used relations. Now I am trying to create them in Navicat. Executing:

ALTER TABLE geerdink_new.dossier 
  ADD CONSTRAINT fk_dossier_klant_1 
    FOREIGN KEY (dossierKlantID) 
    REFERENCES geerdink_new.klant (klantID) 

I am getting some errors:

[Msg] Failed – Error on Foreign Key fk_dossier_klant_1 – 1452 – Cannot add or update a child row: a foreign key constraint fails (geerdink_new.#sql-420_51, CONSTRAINT fk_dossier_klant_1 FOREIGN KEY (dossierKlantID) REFERENCES klant (klantID))

How am I able to solve this?

Answer 1

This is not a Navicat error, but a MySQL error. Something is not matching properly when you’re trying to create your constraint, likely:

1) The column definitions are not identical (for instance one is an unsigned integer, and the other is a signed integer)

2) There are values in one column that do not correspond with values in the column you’re creating a relationship with.

edit: Try this query:

SELECT klantID FROM klant LEFT JOIN geerdink_new ON geerdink_new.dossierKlantId = klant.klantID WHERE dossierKlantId IS NULL;