MySQL外鍵關聯（創世紀新篇）

  

數據庫外鍵

• 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.+---------+----------+------------+---------------------+ 
  27.| city_id | city     | country_id | last_update         | 
  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;
  +---------+----------+------------+---------------------+
  | 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 |
  +------------+---------+---------------------+

  
  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`))

  上面的問題是說由於有關聯的存在，因此沒法改變country_id這個字段。

  而後本身又從新看了下書本，發現本身的sql語句中沒有innodb的外鍵約束方式（cascade,set null,no action,restrict），感受這就是本身出問題的地方。

  但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。就本身找唄，就經過老師說的方法，？ 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

   

  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,...)
  寫了後又是一大堆的錯誤，無從下手啊

   

  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)-----我這裏也創建索引了。網上的說法是：字段類型和外鍵的索引 
  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)-----我這裏也創建索引了。網上的說法是：字段類型和外鍵的索引

   

  這裏是從新創建一張表icity，結果能夠了，總結多是由於字段類型的問題，但是個人alter的問題仍是沒有解決呢：

   

  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)
   
  在你們（老師和網友）的幫助下終於搞定了，作法先drop掉表裏的外鍵，而後在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) 

  大功告成 

  end