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.';
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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 …
Run Code Online (Sandbox Code Playgroud) 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;
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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 …
Run Code Online (Sandbox Code Playgroud) 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';
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