sql - SQL中的交叉外键

Question

我正在尝试使用 2 个带有交叉外键的表，但是在创建它们时不允许引用不存在的表。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延迟外键的评估？

错误是 1005: Can't create table blocks.frm (errno 150) on a mysql 5.0

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 cletus 的答案（完全正确）带到代码中......

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：

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