There could be possibly something you missed or configured in different way. Mysql> INSERT INTO `studentmgmt`.`course_inscription` (`idSubject`, `idStudent`, `Classroom`) VALUES ('1', '1', '12') ĮRROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`studentmgmt`.`course_inscription`, CONSTRAINT `course_inscription_ibfk_1` FOREIGN KEY (`idSubject`) REFERENCES `subject` (`idSubject`)) > FOREIGN KEY (idStudent) REFERENCES student(idStudent) > FOREIGN KEY (idSubject) REFERENCES subject(idSubject), > idSubject INT NOT NULL AUTO_INCREMENT, > idStudent INT NOT NULL AUTO_INCREMENT, For reference: mysql> create database studentmgmt I try to reproduce the error, but MySQL prompting foreign key constraint error. This is not the expected behaviour of MySQL. What did I do wrong to my database? How can I correct the issue? The insert statement: INSERT INTO `studentmgnt`.`course_inscription` The structure and constraints of the relevant database are: CREATE TABLE student (įOREIGN KEY (idSubject) REFERENCES subject(idSubject),įOREIGN KEY (idStudent) REFERENCES student(idStudent) I do not understand why the new row is "added" to the table successfully. When I execute a statement to insert a new row into course_inscription, MySQL must launch the error due to the checking of the foreign key constraint, but it does not work. The length of string types need not be the same.In MySQL, the foreign keys of a table standing for a many to many relationship do not work even though I did set them to the "child" table named course_inscription. The size and sign of integer types must be The cause of our error was due to violation of following rule:Ĭorresponding columns in the foreign key and the referenced key must So if the index in referenced table is exist and it is consists from several columns, and desired column is not first, the error shall be occurred. Where the referenced columns are listed as the first columns in the However, in the referenced table, there must be an index InnoDB permits a foreign key to reference any index column or group ofĬolumns. Referencing table, there must be an index where the foreign keyĬolumns are listed as the first columns in the same order. MySQL requires indexes on foreign keys and referenced keys so thatįoreign key checks can be fast and not require a table scan. Does anyone have any suggestions? And what is meant by first columns? So I guess the problem must be thatĬannot find an index in the referenced table where the referenced columns appear as the first columns.īut I'm not quite sure what this means, or how to check/fix it. (I also tried setting the experiment column to not null, but this didn't fix it). To me, the column types seem to match, since they are both varchar(45). In the table and the referenced table do not match for constraint. Referenced columns appear as the first columns, or column types To get some more information, I did: SHOW ENGINE INNODB STATUS\Gįrom which I got: FOREIGN KEY (experiment) REFERENCES exp (EID)Ĭannot find an index in the referenced table where the Insert_date timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,ĬONSTRAINT FOREIGN KEY (inserted_by) REFERENCES user (iduser),ĬONSTRAINT FOREIGN KEY (target) REFERENCES protein (PID),ĬONSTRAINT FOREIGN KEY (sample_type) REFERENCES sample_type (ID),ĬONSTRAINT FOREIGN KEY (assay) REFERENCES assays (AID),ĬONSTRAINT FOREIGN KEY (experiment) REFERENCES exp (EID)ĮRROR 1215 (HY000): Cannot add foreign key constraint Sample_type mediumint(5) UNSIGNED NOT NULL,Īssay mediumint(5) UNSIGNED ZEROFILL NOT NULL, Step-1: Creating a database university : Here, you will see how to create a database in MySQL as follows. | inserted_by | int(11) unsigned | YES | MUL | NULL | |Īnd I wan't to create a new table called sample_df referencing this, using the following: CREATE TABLE sample_df (ĭf_id mediumint(5) UNSIGNED AUTO_INCREMENT PRIMARY KEY, Steps to add a foreign key using ALTER in MySQL : Here let us see how to add an attribute of student which is the primary key in the student table as a foreign key in another table exam as follows. | Initials | varchar(255) | NO | | NULL | | | EID | varchar(45) | NO | PRI | NULL | | | Field | Type | Null | Key | Default | Extra | I'm having some problems creating a foreign key to an existing table in a MySQL database.
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