执行以下命令时:
ALTER TABLE `mytable` ADD UNIQUE (
`column1` ,
`column2`
);
我得到了这个错误信息:
#1071 - Specified key was too long; max key length is 767 bytes
columnn1和column2的信息:
column1 varchar(20) utf8_general_ci
column2 varchar(500) utf8_general_ci
我认为varchar(20)只需要21个字节，而varchar(500)只需要501个字节。所以总字节数是522，小于767。为什么我得到了错误消息?
#1071 - Specified key was too long; max key length is 767 bytes
当前回答
我解决了这个问题:
varchar(200)
取而代之的是
varchar(191)
所有超过200的唯一或主varchar键将它们替换为191或将它们设置为文本。
其他回答
我在这个话题上做了一些搜索，最后得到了一些自定义更改
MySQL工作台6.3.7版本有图形界面
启动Workbench并选择连接。 转到管理或实例并选择选项文件。 如果Workbench要求您允许读取配置文件，然后按OK两次。 在中心位置的管理员选项文件窗口出现。 进入InnoDB选项卡，如果在General部分没有检查innodb_large_prefix。 设置innodb_default_row_format选项值为DYNAMIC。
对于6.3.7以下的版本，直接选项不可用，因此需要使用命令提示符
Start CMD as administrator. Go To director where mysql server is install Most of cases its at "C:\Program Files\MySQL\MySQL Server 5.7\bin" so command is "cd \" "cd Program Files\MySQL\MySQL Server 5.7\bin". Now Run command mysql -u userName -p databasescheema Now it asked for password of respective user. Provide password and enter into mysql prompt. We have to set some global settings enter the below commands one by one set global innodb_large_prefix=on; set global innodb_file_format=barracuda; set global innodb_file_per_table=true; Now at the last we have to alter the ROW_FORMAT of required table by default its COMPACT we have to set it to DYNAMIC. use following command alter table table_name ROW_FORMAT=DYNAMIC; Done
如果你要创建如下内容:
CREATE TABLE IF NOT EXISTS your_table (
id int(7) UNSIGNED NOT NULL AUTO_INCREMENT,
name varchar(256) COLLATE utf8mb4_bin NOT NULL,
PRIMARY KEY (id),
UNIQUE KEY name (name)
) ENGINE=INNODB DEFAULT CHARSET=utf8mb4 AUTO_INCREMENT=1 ROW_FORMAT=FIXED;
应该是这样的
CREATE TABLE IF NOT EXISTS your_table (
id int(7) UNSIGNED NOT NULL AUTO_INCREMENT,
name varchar(256) COLLATE utf8mb4_bin NOT NULL,
PRIMARY KEY (id)
) ENGINE=INNODB DEFAULT CHARSET=utf8mb4 AUTO_INCREMENT=1 ROW_FORMAT=FIXED;
但是您需要从代码中检查该列的唯一性，或者添加一个新列作为varchar列的MD5或SHA1
我发现这个查询在检测哪些列的索引违反了最大长度方面很有用:
SELECT
c.TABLE_NAME As TableName,
c.COLUMN_NAME AS ColumnName,
c.DATA_TYPE AS DataType,
c.CHARACTER_MAXIMUM_LENGTH AS ColumnLength,
s.INDEX_NAME AS IndexName
FROM information_schema.COLUMNS AS c
INNER JOIN information_schema.statistics AS s
ON s.table_name = c.TABLE_NAME
AND s.COLUMN_NAME = c.COLUMN_NAME
WHERE c.TABLE_SCHEMA = DATABASE()
AND c.CHARACTER_MAXIMUM_LENGTH > 191
AND c.DATA_TYPE IN ('char', 'varchar', 'text')
如果有人在InnoDB和utf8字符集试图在VARCHAR(256)字段上放置UNIQUE索引时遇到问题，请将其切换到VARCHAR(255)字段。255似乎是限制。
您可以添加长列的md5列
