WHERE parent_table.referenced_column IS NULL ON parent_table.referenced_column = child_table.referencing_column Following query would be helpful to fetch those non-matching rows: SELECT child_table.* Now, we can utilize Left Join to find all those rows in the child table, which does not have matching values in the parent table. In most scenarios, we will need to update the data in the child table (instead of deleting them).

However, this is not an option when we already have working/production data in the child table. Some of the other answers are suggesting to delete the data completely from child table, and then apply the constraint.

Sometimes, we may get this error when we are applying Foreign Key constraints to existing table(s), having data in them already. This error generally occurs because we have some values in the referencing field of the child table, which do not exist in the referenced/candidate field of the parent table. I've seen the other posts on this topic, but no luck.Īm I overseeing something or any idea what to do?

Ordrelinje, CONSTRAINT Ordrelinje_fk FOREIGN KEY ( Ordre) REFERENCES Ordre ( OrdreID)) Cannot add or update a child row: a foreign key constraint fails ( srdjank. So when I try to insert values into ORDRELINJE table i get:Įrror Code: 1452. ProduktBeskrivelse VARCHAR(100) DEFAULT NULL,ĬONSTRAINT Produkt_pk PRIMARY KEY (ProduktID)Īnd ORDRELINJE table: CREATE TABLE Ordrelinje (ĬONSTRAINT Ordrelinje_pk PRIMARY KEY (Ordre, Produkt),ĬONSTRAINT Ordrelinje_fk FOREIGN KEY (Ordre) REFERENCES Ordre (OrdreID),ĬONSTRAINT Ordrelinje_fk1 FOREIGN KEY (Produkt) REFERENCES Produkt (ProduktID) I have created tables in MySQL Workbench as shown below :ĬONSTRAINT Ordre_pk PRIMARY KEY (OrdreID),ĬONSTRAINT Ordre_fk FOREIGN KEY (KundeID) REFERENCES Kunde (KundeID)

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