MySQL Error 150

Question

Я пытаюсь создать скрипт для нормализации другой таблицы в MySQL.Вот что у меня есть:

USE  hw7;

SET foreign_key_checks = 0;
DROP TABLE IF EXISTS airport_codes;
DROP TABLE IF EXISTS airport_locations;
DROP TABLE IF EXISTS airport_codenames;
SET foreign_key_checks = 1;

CREATE TABLE airport_codes(
airport_code char(3) not null,
airline_code char(2) not null,
primary key (airport_code, airline_code)
);

INSERT INTO airport_codes SELECT DISTINCT airport_code, airline_code 
    FROM airport_airlines;

CREATE TABLE airport_locations(
airport_code char(3) not null,
city varchar(20) not null,
state char(2) not null,
primary key (airport_code),
constraint ap_code_fk
    foreign key (airport_code)
    references airport_codes(airport_code)
);

INSERT INTO airport_locations SELECT DISTINCT airport_code, city, state 
    FROM airport_airlines;

CREATE TABLE airport_codenames(
airline_code char(2) not null,
name varchar(20) not null,
primary key (airline_code),
constraint al_code_fk
    foreign key (airline_code)
    references airport_codes(airline_code)
);

INSERT INTO airport_codenames SELECT DISTINCT airline_code, name 
    FROM airport_airlines;

Этот код приводит к этой ошибке:

Невозможно создать таблицу hw7.airport_codenames errno: 150

Answer 1

Поскольку airport_codes имеет несколько возможных строк на airport_code и airline_code (как составной ключ), другие внешние ключи не могут ссылаться на него.Переместите отношения FK в airport_codes, указывая на airport_locations и airport_codenames.

USE  hw7;

SET foreign_key_checks = 0;
DROP TABLE IF EXISTS airport_codes;
DROP TABLE IF EXISTS airport_locations;
DROP TABLE IF EXISTS airport_codenames;
SET foreign_key_checks = 1;


CREATE TABLE airport_locations(
airport_code char(3) not null,
city varchar(20) not null,
state char(2) not null,
primary key (airport_code)
);

INSERT INTO airport_locations SELECT DISTINCT airport_code, city, state 
    FROM airport_airlines;

CREATE TABLE airport_codenames(
airline_code char(2) not null,
name varchar(20) not null,
primary key (airline_code)
);

INSERT INTO airport_codenames SELECT DISTINCT airline_code, name 
    FROM airport_airlines;


/* airport_codes moved after the other 2 tables, and FKs defined here */
CREATE TABLE airport_codes(
airport_code char(3) not null,
airline_code char(2) not null,
primary key (airport_code, airline_code),
/* FK relationships are defined here, rather than in the other tables,
   since the PKs for airport_code and airline_code are defined in the
   other tables.
*/
constraint ap_code_fk
    foreign key (airport_code)
    references airport_locations (airport_code),
constraint al_code_fk
    foreign key (airline_code)
    references airport_codenames (airline_code)
);

INSERT INTO airport_codes SELECT DISTINCT airport_code, airline_code 
    FROM airport_airlines;

Answer 2

Должен исходить от вас порядок столов дропа. Как MySQL Док сказать

InnoDB не разрешает вам отбрасывать таблицу, на которую ссылается ограничение FOREIGN KEY, если вы не установили SET foreign_key_checks = 0

Поэтому установите проверку внешнего ключа по праву или измените порядок сброса на:

DROP TABLE IF EXISTS airport_locations;
DROP TABLE IF EXISTS airport_codenames;
DROP TABLE IF EXISTS airport_codes;

Вы опускаете внешний ключ перед ссылкой.