ERROR 1452: Cannot add or update a child row: a fo

Question

I have created tables in MySQL Workbench as shown below :

ORDRE table:

CREATE TABLE Ordre (
  OrdreID   INT NOT NULL,
  OrdreDato DATE DEFAULT NULL,
  KundeID   INT  DEFAULT NULL,
  CONSTRAINT Ordre_pk PRIMARY KEY (OrdreID),
  CONSTRAINT Ordre_fk FOREIGN KEY (KundeID) REFERENCES Kunde (KundeID)
)
  ENGINE = InnoDB;

PRODUKT table:

CREATE TABLE Produkt (
  ProduktID          INT NOT NULL,
  ProduktBeskrivelse VARCHAR(100) DEFAULT NULL,
  ProduktFarge       VARCHAR(20)  DEFAULT NULL,
  Enhetpris          INT          DEFAULT NULL,
  CONSTRAINT Produkt_pk PRIMARY KEY (ProduktID)
)
  ENGINE = InnoDB;

and ORDRELINJE table:

CREATE TABLE Ordrelinje (
  Ordre         INT NOT NULL,
  Produkt       INT NOT NULL,
  AntallBestilt INT DEFAULT NULL,
  CONSTRAINT Ordrelinje_pk PRIMARY KEY (Ordre, Produkt),
  CONSTRAINT Ordrelinje_fk FOREIGN KEY (Ordre) REFERENCES Ordre (OrdreID),
  CONSTRAINT Ordrelinje_fk1 FOREIGN KEY (Produkt) REFERENCES Produkt (ProduktID)
)
  ENGINE = InnoDB;

so when I try to insert values into ORDRELINJE table i get:

Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (srdjank.Ordrelinje, CONSTRAINT Ordrelinje_fk FOREIGN KEY (Ordre) REFERENCES Ordre (OrdreID))

I've seen the other posts on this topic, but no luck. Am I overseeing something or any idea what to do?

Answer 1

While inserting the foreign key attribute values, first verify the attributes type, as well as primary key attribute value in the parent relation, if the values in parent relation matches, then you can easily insert/update child attribute values.

Answer 2

Your ORDRELINJE table is linked with ORDER table using a foreign key constraint constraint Ordrelinje_fk foreign key(Ordre) references Ordre(OrdreID) according to which Ordre int NOT NULL, column of table ORDRELINJE must match any Ordre int NOT NULL, column of ORDER table.

Now what is happening here is, when you are inserting new row into ORDRELINJE table, according to fk constraint Ordrelinje_fk it is checking ORDER table if the OrdreID is present or not and as it is not matching with any OrderId, Compiler is complaining for foreign key violation. This is the reason you are getting this error.

Foreign key is the primary key of the other table which you use in any table to link between both. This key is bound by the foreign key constraint which you specify while creating the table. Any operation on the data must not violate this constraint. Violation of this constraint may result in errors like this.

Hope I made it clear.