MySQL错误无法添加外键约束 [英] MySQL error cannot add foreign key constraint

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问题描述

怎么了?

mysql> create table price(
    -> p_code char(1) not null,
    -> p_description varchar(20),
    -> p_rentfee decimal(2,2) not null,
    -> p_dylatefee decimal(2,2));
Query OK, 0 rows affected (0.18 sec)

mysql> create table movie(
    -> mv_no char(4) not null,
    -> mv_name varchar(50) not null,
    -> mv_year char(4) not null,
    -> mv_cost decimal(2,2) not null,
    -> mv_genre varchar(15) not null,
    -> p_code char(1) not null,
    -> foreign key (p_code) references price(p_code));
ERROR 1215 (HY000): Cannot add foreign key constraint

mysql>

推荐答案

price.p_code不是price的主键.试试:

create table price(
p_code char(1) not null PRIMARY KEY,
p_description varchar(20),
p_rentfee decimal(2,2) not null,
p_dylatefee decimal(2,2));

通常,外键必须引用主键/唯一键,整个主键/唯一键,并且只能引用主键/唯一键.

In general, foreign keys must reference a primary/unique key, a whole primary/unique key, and nothing but a primary/unique key.

在某些RDBMS(例如SQL Server)中,您可以引用具有唯一 index (不是键)的列(请参见

In some RDBMS, for example SQL Server, you can reference a column with a unique index (not key) (see can we have a foreign key which is not a primary key in any other table?), but this is non-standard behavior.

这篇关于MySQL错误无法添加外键约束的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!

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