当我执行以下命令时:
ALTER TABLE `mytable` ADD UNIQUE (
`column1` ,
`column2`
);
我收到此错误消息:
#1071 - Specified key was too long; max key length is 767 bytes
有关column1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。因此,总字节数是522,少于767。那么为什么收到错误消息?
#1071 - Specified key was too long; max key length is 767 bytes