Question

我有以下查询：

create table bans
(
    id int auto_increment primary key ,
    reason int not null,
    player int not null,
    server int not null,
    starts timestamp default current_timestamp not null,
    ends DATETIME not null,
    constraint bans__fk_player
        foreign key (player) references players ('id'),
    constraint bans__fk_server
        foreign key (server) references servers ('id')
);

这将导致：

[2019-01-02 18:35:29] [42000][1064] (conn=75) You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ''id'),
[2019-01-02 18:35:29] [42000][1064] You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ''id'),

我只想在两者之间建立1：n关系：

players.id-> bans.player 并命名为bans__fk_player

servers.id-> bans.server 并命名为bans__fk_server

Answer 1

1）SO人员已经对此进行了评论：您需要在外键定义中删除标识符周围的引号。有关在mysql / MariaDB中使用引号的一般性讨论，另请参见this SO post。

2）另一个问题是您没有正确定义约束，它缺少外键的名称。语法如下，如this mysql turorial中所述：

CONSTRAINT constraint_name
FOREIGN KEY foreign_key_name (columns)
REFERENCES parent_table(columns)

因此您的代码应为：

...
constraint bans__player
    foreign key bans__fk_player (player) references players (id),
constraint bans__server
    foreign key bans__fk_server (server) references servers (id)
...

请参见this db fiddle。

这也应该工作，并且产生较短的语法（您可能不需要显式地命名约束）：

...
foreign key bans__fk_player (player) references players (id),
foreign key bans__fk_server (server) references servers (id)
...

如果仍然遇到错误，则必须查看引用表（服务器和播放器）的定义。在两个表中，id必须是表的主键，或者必须由唯一约束控制。当然，它必须是数字。

Answer 2

如果您想引用列id，在MariaDB（同样在MySQL）中，您应使用“回勾”，如：

create table bans
(
    id int auto_increment primary key ,
    reason int not null,
    player int not null,
    server int not null,
    starts timestamp default current_timestamp not null,
    ends DATETIME not null,
    constraint bans__fk_player
        foreign key (player) references players (`id`),
    constraint bans__fk_server
        foreign key (server) references servers (`id`)
);

MariaDB-无法使用两个外键创建表

2 个答案: