相关疑难解决方法(0)

我的研究和实验尚未得出答案,所以我希望得到一些帮助.

我正在修改应用程序的安装文件,在以前的版本中没有我想要添加的列.我不想手动添加列,而是在安装文件中,并且只有在表中不存在新列时才这样.

该表创建如下:

CREATE TABLE IF NOT EXISTS `#__comm_subscribers` (
      `subscriber_id` int(11) NOT NULL auto_increment,
      `user_id` int(11) NOT NULL default '0',
      `subscriber_name` varchar(64) NOT NULL default '',
      `subscriber_surname` varchar(64) NOT NULL default '',
      `subscriber_email` varchar(64) NOT NULL default '',
      `confirmed` tinyint(1) NOT NULL default '0',
      `subscribe_date` datetime NOT NULL default '0000-00-00 00:00:00',
      PRIMARY KEY  (`subscriber_id`),
      UNIQUE KEY `subscriber_email` (`subscriber_email`)
    ) ENGINE=MyISAM CHARACTER SET 'utf8' COLLATE 'utf8_general_ci' COMMENT='Subscribers for Comm are stored here.';

如果我在create table语句下添加以下内容,那么我不确定如果列已经存在(并且可能已填充)会发生什么:

ALTER TABLE `#__comm_subscribers` ADD `subscriber_surname`;
ALTER …

IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
  WHERE TABLE_NAME = 'email_subscription' AND COLUMN_NAME = 'subscribe_all')
  THEN 
  ALTER TABLE email_subscription
  ADD COLUMN subscribe_all TINYINT(1) DEFAULT 1,
  ADD COLUMN subscribe_category varchar(512) DEFAULT NULL;

我看了很多例子.但是这个查询不起作用,我得到的错误是:

错误1064(42000):您的SQL语法有错误; 查看与您的MySQL服务器版本对应的手册,以便在'IF NOT EXISTS(SELECT*FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME =')第1行附近使用正确的语法

在我的数据库创建脚本中创建脚本,如下所示:

CREATE TABLE IF NOT EXISTS `rabbits`
(
    `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
    `name` VARCHAR(255) NOT NULL,
    `main_page_id` INT UNSIGNED COMMENT 'What page is the main one',
    PRIMARY KEY (`id`),
    KEY `main_page_id` (`main_page_id`)
)
ENGINE=InnoDB;

CREATE TABLE IF NOT EXISTS `rabbit_pages`
(
    `id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
    `rabbit_id` INT UNSIGNED NOT NULL,
    `title` VARCHAR(255) NOT NULL,
    `content` TEXT NOT NULL,
    PRIMARY KEY (`id`),
    KEY `rabbit_id` (`rabbit_id`),
    CONSTRAINT `fk_rabbits_pages` FOREIGN KEY (`rabbit_id`) REFERENCES `rabbits` (`id`)
)
ENGINE=InnoDB;

ALTER TABLE …

我想在表中添加一列,但如果它已经添加到表中,我不希望它失败.我怎样才能做到这一点？

# Add column fails if it already exists 
ALTER TABLE `TableName` ADD `ColumnName` int(1) NOT NULL default '0';