Question

我正在尝试使用带有交叉外键的2个表，但我不允许在创建它时引用不存在的表。有什么方法可以为mysql创建这样的表，比如同时声明两个表或者延迟评估外键？

错误是1005：无法在mysql 5.0上创建表blocks.frm（errno 150）

SQL：

create table if not exists blocks( 
    id int unsigned not null auto_increment, 
    title varchar(100),
    defaultpage int unsigned not null, 
    foreign key(defaultpage) references pages(pageID), 
    primary key(id)) engine=innodb;

create table if not exists pages( 
    pageID int unsigned not null auto_increment, 
    title varchar(50) not null, 
    content blob,  
    blockid int unsigned not null, 
    foreign key(blockid) references block(id), 
    primary key(pageID) ) engine=innodb;

解决问题的正确方法是什么？

Answer 1

将克拉图斯的答案（这是完全正确的）带到代码......

create table if not exists pages( 
    pageID int unsigned not null auto_increment, 
    title varchar(50) not null, 
    content blob,  
    blockid int unsigned not null, 
    primary key(pageID) ) engine=innodb;

create table if not exists blocks( 
    id int unsigned not null auto_increment, 
    title varchar(100),
    defaultpage int unsigned not null, 
    foreign key(defaultpage) references pages(pageID), 
    primary key(id)) engine=innodb;

alter table pages add constraint fk_pages_blockid foreign key (blockid) references blocks (id);

Answer 2

您可以延迟外键检查，直到创建表格为止：

SET FOREIGN_KEY_CHECKS = 0;
CREATE TABLE ...;
SET FOREIGN_KEY_CHECKS = 1;

SQL中交叉的外键

2 个答案: