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 程式師世界 >> 數據庫知識 >> MYSQL數據庫 >> MySQL綜合教程 >> 深入mysql外鍵關聯問題的詳解

深入mysql外鍵關聯問題的詳解

編輯:MySQL綜合教程

今兒繼續再看老師給推薦的深入淺出mysql數據庫開發這本書,看到innodb數據庫的外鍵關聯問題時,遇到了一個問題,書上寫的是可以對父表進行修改,從而同步到子表的外鍵上去,可是自己的實驗卻是沒有能夠。
復制代碼 代碼如下:
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;
+---------+----------+------------+---------------------+
| city_id | city     | country_id | last_update         |
+---------+----------+------------+---------------------+
|       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 |
+------------+---------+---------------------+

復制代碼 代碼如下:
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`))

上面的問題是說因為有關聯的存在,所以無法改變country_id這個字段。
然後自己又重新看了下書本,發現自己的sql語句中沒有innodb的外鍵約束方式(cascade,set null,no action,restrict),感覺這就是自己出問題的地方。
可是怎麼加入關聯方式呢,上網找了好半天也沒有合適的方法。就自己找呗,就通過老師說的方法,? help一點兒一點兒終於找到了怎麼改變的方法,文檔功能很強大啊
復制代碼 代碼如下:
| 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,...)

寫了後又是一大堆的錯誤,無從下手啊
復制代碼 代碼如下:
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)-----我這裡也建立索引了。網上的說法是:字段類型和外鍵的索引

這裡是重新建立一張表icity,結果可以了,總結可能是因為字段類型的問題,可是我的alter的問題還是沒有解決呢:
復制代碼 代碼如下:
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(老師和網友)的幫助下終於搞定了,做法先drop掉表裡的外鍵,然後在add。呵呵……
復制代碼 代碼如下:
mysql> alter table city drop FOREIGN KEY `city_ibfk_1`;
Query OK, 0 rows affected (0.24 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> alter table city add FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE;Query OK, 0 rows affected (0.16 sec)
Records: 0  Duplicates: 0  Warnings: 0
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`),
  KEY `idx_fk_country_id` (`country_id`),
  CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

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