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主题： [转帖]mysql外键关联问题

napolenAx

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2014-12-10 11:44:55 | [全部帖] [楼主帖]

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01.mysql> show create table country\G

02.*************************** 1. row ***************************

03. Table: country

04.Create Table: CREATE TABLE `country` (

05. `country_id` smallint(5) unsigned NOT NULL auto_increment,

06. `country` varchar(50) NOT NULL,

07. `last_update` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,

08. PRIMARY KEY (`country_id`)

09.) ENGINE=InnoDB DEFAULT CHARSET=utf8

10.1 row in set (0.01 sec)

11.

12.mysql> show create table city\G

13.*************************** 1. row ***************************

14. Table: city

15.Create Table: CREATE TABLE `city` (

16. `city_id` smallint(5) unsigned NOT NULL auto_increment,

17. `city` varchar(50) NOT NULL,

18. `country_id` smallint(5) unsigned NOT NULL,

19. `last_update` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,

20. PRIMARY KEY (`city_id`),

21. KEY `country_id` (`country_id`),

22. CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`)

23.) ENGINE=InnoDB DEFAULT CHARSET=utf8

24.1 row in set (0.00 sec)

25.mysql> select * from city;

26.+---------+----------+------------+---------------------+

28.+---------+----------+------------+---------------------+

29.| 1 | hancheng | 1 | 2012-01-09 09:18:33 |

30.+---------+----------+------------+---------------------+

31.1 row in set (0.01 sec)

32.

33.mysql> select * from country;

34.+------------+---------+---------------------+

35.| country_id | country | last_update |

36.+------------+---------+---------------------+

37.| 1 | chen | 2012-01-09 09:16:38 |

38.+------------+---------+---------------------+

mysql> show create table country\G

*************************** 1. row ***************************

Table: country

Create Table: CREATE TABLE `country` (

`country_id` smallint(5) unsigned NOT NULL auto_increment,

`country` varchar(50) NOT NULL,

`last_update` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,

PRIMARY KEY (`country_id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8

1 row in set (0.01 sec)

mysql> show create table city\G

*************************** 1. row ***************************

Table: city

Create Table: CREATE TABLE `city` (

`city_id` smallint(5) unsigned NOT NULL auto_increment,

`city` varchar(50) NOT NULL,

`country_id` smallint(5) unsigned NOT NULL,

`last_update` timestamp NOT NULL default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP,

PRIMARY KEY (`city_id`),

KEY `country_id` (`country_id`),

CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8

1 row in set (0.00 sec)

mysql> select * from city;

+---------+----------+------------+---------------------+

+---------+----------+------------+---------------------+

| 1 | hancheng | 1 | 2012-01-09 09:18:33 |

+---------+----------+------------+---------------------+

1 row in set (0.01 sec)

mysql> select * from country;

+------------+---------+---------------------+

| country_id | country | last_update |

+------------+---------+---------------------+

| 1 | chen | 2012-01-09 09:16:38 |

+------------+---------+---------------------+

01.mysql> update country set country_id=100 where country_id=1;

02.ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`test/city`, CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`))

mysql> update country set country_id=100 where country_id=1;

ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`test/city`, CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`))

上面的问题是说因为有关联的存在，所以无法改变country_id这个字段。

然后自己又重新看了下书本，发现自己的sql语句中没有innodb的外键约束方式（cascade,set null,no action,restrict），感觉这就是自己出问题的地方。

可是怎么加入关联方式呢，上网找了好半天也没有合适的方法。就自己找呗，就通过老师说的方法，？ help一点儿一点儿终于找到了怎么改变的方法，文档功能很强大啊

01.| ADD {INDEX|KEY} [index_name] [index_type] (index_col_name,...)

02. | ADD [CONSTRAINT [symbol]]

03. PRIMARY KEY [index_type] (index_col_name,...)

04. | ADD [CONSTRAINT [symbol]]

05. UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name,...)

| ADD {INDEX|KEY} [index_name] [index_type] (index_col_name,...)

| ADD [CONSTRAINT [symbol]]

PRIMARY KEY [index_type] (index_col_name,...)

| ADD [CONSTRAINT [symbol]]

UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name,...)

写了后又是一大堆的错误，无从下手啊

01.mysql> alter table city add CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE;

02.ERROR 1005 (HY000): Can't create table '.\test\#sql-ed0_37.frm' (errno: 121)

03.zhouqian@zhou:~$ perror 121

04.OS error code 121: Remote I/O error

05.MySQL error code 121: Duplicate key on write or update

06.

07.Can't create table 'test.icity' (errno: 150)-----我这里也建立索引了。网上的说法是：字段类型和外键的索引

mysql> alter table city add CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE;

ERROR 1005 (HY000): Can't create table '.\test\#sql-ed0_37.frm' (errno: 121)

zhouqian@zhou:~$ perror 121

OS error code 121: Remote I/O error

MySQL error code 121: Duplicate key on write or update

Can't create table 'test.icity' (errno: 150)-----我这里也建立索引了。网上的说法是：字段类型和外键的索引

这里是重新建立一张表icity，结果可以了，总结可能是因为字段类型的问题，可是我的alter的问题还是没有解决呢：

01.mysql> create table icity(id int not null, city varchar(20), country_id smallint unsigned not null , primary key(id), foreign key(country_id) references country(country_id) on update cascade )engine=innodb;

02.Query OK, 0 rows affected (0.11 sec)

03.

04.mysql> show create table icity\G

05.*************************** 1. row ***************************

06. Table: icity

07.Create Table: CREATE TABLE `icity` (

08. `id` int(11) NOT NULL,

09. `city` varchar(20) DEFAULT NULL,

10. `country_id` smallint(5) unsigned NOT NULL,

11. PRIMARY KEY (`id`),

12. KEY `country_id` (`country_id`),

13. CONSTRAINT `icity_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE

14.) ENGINE=InnoDB DEFAULT CHARSET=latin1

15.1 row in set (0.02 sec)

mysql> create table icity(id int not null, city varchar(20), country_id smallint unsigned not null , primary key(id), foreign key(country_id) references country(country_id) on update cascade )engine=innodb;

Query OK, 0 rows affected (0.11 sec)

mysql> show create table icity\G

*************************** 1. row ***************************

Table: icity

Create Table: CREATE TABLE `icity` (

`id` int(11) NOT NULL,

`city` varchar(20) DEFAULT NULL,

`country_id` smallint(5) unsigned NOT NULL,

PRIMARY KEY (`id`),

KEY `country_id` (`country_id`),

CONSTRAINT `icity_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE

) ENGINE=InnoDB DEFAULT CHARSET=latin1

1 row in set (0.02 sec)

在大家（老师和网友）的帮助下终于搞定了，做法先drop掉表里的外键，然后在add。呵呵……

01.mysql> alter table city drop FOREIGN KEY `city_ibfk_1`;

02.Query OK, 0 rows affected (0.24 sec)

03.Records: 0 Duplicates: 0 Warnings: 0

04.

05.mysql> alter table city add FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE;Query OK, 0 rows affected (0.16 sec)

06.Records: 0 Duplicates: 0 Warnings: 0

07.

08.mysql> show create table city\G

09.*************************** 1. row ***************************

10. Table: city

11.Create Table: CREATE TABLE `city` (

12. `city_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,

13. `city` varchar(50) NOT NULL,

14. `country_id` smallint(5) unsigned NOT NULL,

15. `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,

16. PRIMARY KEY (`city_id`),

17. KEY `country_id` (`country_id`),

18. KEY `idx_fk_country_id` (`country_id`),

19. CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE

20.) ENGINE=InnoDB DEFAULT CHARSET=utf8

21.1 row in set (0.00 sec)

--转自

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