mysql> create table cc(id int auto_increment); ERROR (): Incorrect table definition; there can be only one auto column and it must be def ined as a key mysql> create table cc(id int auto_increment primary key); Query OK, rows affected (0.03 sec) mys
1.错误描述 10:10:38 alter table user add num int(8) primary key first Error Code: 1068. Multiple primary key defined 0.000 sec 2.错误原因 这个错误的原因是定义了两个主键,导致出错 3.解决办法 alter table user add num int(8) primary key first; 去掉"primary key"
When I have do some sql tody, some confusion come up to me. Its about the index && PRIMARY KEY && UNIQUE KEY in MySQL. So I google it for the answers. There is a clearly answer on the StackOverflow. So I share it on this BLOG. About INDEX:
官方的解释: The error happens because MySQL can index only the first N chars of a BLOB or TEXT column. So The error mainly happen when there is a field/column type of TEXT or BLOB or those belongs to TEXT or BLOB types such as TINYBLOB, MEDIUMBLOB, LONGBL
参考:MySQL中KEY.PRIMARY KEY.UNIQUE KEY.INDEX 的区别 对于题目中提出的问题,可以拆分来一步步解决.在 MySQL 中 KEY 和 INDEX 是同义.那这个问题就可以简化为 PRIMARY KEY,UNIQUE KEY 和 INDEX 的区别.而这三者也正好是索引的划分,主键索引,唯一索引和普通索引(INDEX). 使用 INDEX 来加速从数据库中读取数据.INDEX 通常加在那些 JOIN, WHERE,和 ORDER BY 子句的列上. 创建索引时,需