MySQL Error 150 | 易学教程

问题

I'm trying to create a script to normalize another table in MySQL. Below is what I have:

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;

This code results in this error:

Can't create table hw7.airport_codenames errno:150

回答1:

Since airport_codes has multiple possible rows per airport_code and airline_code (as a composite key), it cannot be referenced by other foreign keys. Move the FK relationships into airport_codes, pointing to airport_locations and 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;

回答2:

It should come from you drop table order. Like mysql doc say

InnoDB does not permit you to drop a table that is referenced by a FOREIGN KEY constraint, unless you do SET foreign_key_checks = 0

So set the foreign key check rightfully or change your drop order in:

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

You drop foreign key before the reference.

来源：https://stackoverflow.com/questions/9865992/mysql-error-150

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mysql

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mysql-error-1005