SOLVED: By removing the primary key atribute from the foreign keys.
I'm building an SQL Database for an school, to keep track of teachers, students, groups and payments.
I have set all the foreign keys to cascade on update (since I believe it's going to be the best way), but I want to set them to null on delete (ie: if someones deletes a group, students can be assigned to another group with an update), but the server gives me this message in tables grupo and grupoalumno when I try to create the database:
Error: 150 "Foreign key constraint is incorrectly formed".
I have the foreign keys with not null unchecked (which means a foreign key can be a null value), and from what I understood, solution is to set the primary keys being referenced as being able to be null, which makes me question if it would be a good idea to have a PK null.
I have also considered restricting the delete, and only using updates (ie: editing a group until it's right instead of deleting it), but I think being able to actually delete a group without cascading the whole database would be wise.
I'm creating the tables in the order they need to be (ie: not creating a table that references a key that hasn't been created yet.
I'm using PHPMyAdmin and MySQL Workbench. I believe MySQL exports the database with InnoDB as the engine.
I hope I explained myself. Thanks in advance. Hoping to learn a lot!
Code:
-- MySQL Script generated by MySQL Workbench
-- 10/29/18 21:25:26
-- Model: New Model Version: 1.0
SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0;
SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES';
-- -----------------------------------------------------
-- Schema celex
-- -----------------------------------------------------
CREATE SCHEMA IF NOT EXISTS `celex` DEFAULT CHARACTER SET utf8 COLLATE utf8_spanish_ci ;
USE `celex` ;
-- -----------------------------------------------------
-- Table `celex`.`Grupo`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`Grupo` (
`idGrupo` INT NOT NULL AUTO_INCREMENT,
`idioma` VARCHAR(45) NOT NULL,
`nivel` VARCHAR(45) NOT NULL,
`horarioInicio` TIME NULL,
`horarioTermino` TIME NULL,
PRIMARY KEY (`idGrupo`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `celex`.`Alumno`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`Alumno` (
`idAlumno` INT NOT NULL AUTO_INCREMENT,
`nombre` VARCHAR(45) NOT NULL,
`primerApellido` VARCHAR(45) NOT NULL,
`segundoApellido` VARCHAR(45) NOT NULL,
`email` VARCHAR(45) NOT NULL,
`telefono` VARCHAR(45) NULL,
`edad` INT NULL,
`procedencia` VARCHAR(45) NULL,
`fechaIngreso` DATE NOT NULL,
`nivelIngreso` VARCHAR(45) NOT NULL,
`moduloIngreso` INT NOT NULL,
`nivelColocacion` VARCHAR(45) NULL,
`moduloColocacion` INT NULL,
PRIMARY KEY (`idAlumno`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `celex`.`Periodo`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`Periodo` (
`idPeriodo` INT NOT NULL AUTO_INCREMENT,
`nombre` VARCHAR(45) NULL,
`inicio` DATE NOT NULL,
`termino` DATE NOT NULL,
PRIMARY KEY (`idPeriodo`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `celex`.`GrupoAlumno`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`GrupoAlumno` (
`idGrupoAlumno` INT NOT NULL AUTO_INCREMENT,
`modulo` INT NOT NULL,
`calificacionParcial` DOUBLE NULL,
`calificacionFinal` DOUBLE NULL,
`calificacionExtra` DOUBLE NULL,
`Periodo_idPeriodo` INT NULL,
`Grupo_idGrupo` INT NULL,
`Alumno_idAlumno` INT NULL,
PRIMARY KEY (`idGrupoAlumno`, `Periodo_idPeriodo`, `Grupo_idGrupo`, `Alumno_idAlumno`),
INDEX `fk_Grupo_has_Alumno_Alumno1_idx` (`Alumno_idAlumno` ASC),
INDEX `fk_Grupo_has_Alumno_Grupo_idx` (`Grupo_idGrupo` ASC),
INDEX `fk_GrupoAlumno_Periodo1_idx` (`Periodo_idPeriodo` ASC),
CONSTRAINT `fk_Grupo_has_Alumno_Grupo`
FOREIGN KEY (`Grupo_idGrupo`)
REFERENCES `celex`.`Grupo` (`idGrupo`)
ON DELETE SET NULL
ON UPDATE CASCADE,
CONSTRAINT `fk_Grupo_has_Alumno_Alumno1`
FOREIGN KEY (`Alumno_idAlumno`)
REFERENCES `celex`.`Alumno` (`idAlumno`)
ON DELETE SET NULL
ON UPDATE CASCADE,
CONSTRAINT `fk_GrupoAlumno_Periodo1`
FOREIGN KEY (`Periodo_idPeriodo`)
REFERENCES `celex`.`Periodo` (`idPeriodo`)
ON DELETE SET NULL
ON UPDATE CASCADE)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `celex`.`PeriodoAlumno`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`PeriodoAlumno` (
`idPeriodoAlumno` INT NOT NULL AUTO_INCREMENT,
`cuota` TINYINT(1) NULL,
`Periodo_idPeriodo` INT NULL,
`Alumno_idAlumno` INT NULL,
PRIMARY KEY (`idPeriodoAlumno`, `Periodo_idPeriodo`, `Alumno_idAlumno`),
INDEX `fk_Periodo_has_Alumno_Alumno1_idx` (`Alumno_idAlumno` ASC),
INDEX `fk_Periodo_has_Alumno_Periodo1_idx` (`Periodo_idPeriodo` ASC),
CONSTRAINT `fk_Periodo_has_Alumno_Periodo1`
FOREIGN KEY (`Periodo_idPeriodo`)
REFERENCES `celex`.`Periodo` (`idPeriodo`)
ON DELETE SET NULL
ON UPDATE CASCADE,
CONSTRAINT `fk_Periodo_has_Alumno_Alumno1`
FOREIGN KEY (`Alumno_idAlumno`)
REFERENCES `celex`.`Alumno` (`idAlumno`)
ON DELETE SET NULL
ON UPDATE CASCADE)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `celex`.`Maestro`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`Maestro` (
`idMaestro` INT NOT NULL AUTO_INCREMENT,
`nombre` VARCHAR(45) NOT NULL,
`primerApellido` VARCHAR(45) NOT NULL,
`segundoApellido` VARCHAR(45) NOT NULL,
`email` VARCHAR(45) NOT NULL,
`telefono` VARCHAR(45) NULL,
PRIMARY KEY (`idMaestro`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `celex`.`GrupoMaestro`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `celex`.`GrupoMaestro` (
`idGrupoMaestro` INT NOT NULL AUTO_INCREMENT,
`Grupo_idGrupo` INT NULL,
`Maestro_idMaestro` INT NULL,
PRIMARY KEY (`idGrupoMaestro`, `Grupo_idGrupo`, `Maestro_idMaestro`),
INDEX `fk_Grupo_has_Maestro_Maestro1_idx` (`Maestro_idMaestro` ASC),
INDEX `fk_Grupo_has_Maestro_Grupo1_idx` (`Grupo_idGrupo` ASC),
CONSTRAINT `fk_Grupo_has_Maestro_Grupo1`
FOREIGN KEY (`Grupo_idGrupo`)
REFERENCES `celex`.`Grupo` (`idGrupo`)
ON DELETE SET NULL
ON UPDATE CASCADE,
CONSTRAINT `fk_Grupo_has_Maestro_Maestro1`
FOREIGN KEY (`Maestro_idMaestro`)
REFERENCES `celex`.`Maestro` (`idMaestro`)
ON DELETE SET NULL
ON UPDATE CASCADE)
ENGINE = InnoDB;
SET SQL_MODE=@OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS;
edit: Appending query to create database.
When setting the Foreign Key constraint, in addition to cascade on update you can define to set null on delete like this:
FOREIGN KEY (Grupo_idGrupo) REFERENCES Grupo (idGrupo)
ON DELETE SET NULL ON UPDATE CASCADE
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