MySQL 将文本列设为唯一键
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make text column as unique key
提问by d-doctor
i want to make a table in MySQLserver with mediumtextcolumn as UNIQUE KEY
我想在MySQL服务器中制作一个表，mediumtext列为UNIQUE KEY
CREATE TABLE `parts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` mediumtext NOT NULL,
`display_status` int(11) NOT NULL,
UNIQUE KEY `name` (`name`),
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
but this made an error
但这犯了一个错误
BLOB/TEXT column 'name' used in key specification without a key length
when I change the type of `name` to varchar .. it works!
当我将 `name` 的类型更改为 varchar 时..它起作用了！
can you tell if i can to make text column as UNIQUE KEY
你能告诉我是否可以将文本列设为 UNIQUE KEY
回答by Mari
Basically you can not use Textcolumn as UNIQUEkey. Because practically such a big column will not be unique and there might be a chance of more duplicates. So go for hashingmethod and use that output as a UNIQUE constraint.
基本上你不能使用Text列作为UNIQUE键。因为实际上如此大的列不会是唯一的，并且可能有更多重复的机会。所以转到hashing方法并将该输出用作唯一约束。
Hope this helps you
希望这对你有帮助
回答by Bohemian
The limit of 255 for varchar length no longer applies. From the documentation:
varchar 长度的 255 限制不再适用。从文档：
Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in 5.0.3 and later versions.
VARCHAR 列中的值是可变长度的字符串。在 MySQL 5.0.3 之前，长度可以指定为 0 到 255 之间的值，在 5.0.3 及更高版本中可以指定为 0 到 65,535。
Unique indexes must have a known maximum length (a requirement of mysql due to its internal implementation), so use varchar with a large enough value to fit your longest expected value, eg
唯一索引必须具有已知的最大长度（mysql 由于其内部实现而要求），因此使用具有足够大值的 varchar 以适合您最长的期望值，例如
...
`name` varchar(65535) NOT NULL, -- for example
...
