mysql - 需要帮助理解这段 MySQL 代码

Question

CREATE TABLE `users` (
`ID` int(10) unsigned zerofill NOT NULL auto_increment,
`username` varchar(20) NOT NULL,
PRIMARY KEY  (`ID`),
KEY `Username` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

什么是a) 未签名，在 ID 表中填零？b) KEY Username (username) 是什么意思？

谢谢

Answer 1

zerofill - 左填充 0

For example, for a column declared as INT(4) ZEROFILL, a value of 5 is retrieved as 0005.

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无符号数不小于零

If you specify ZEROFILL for a numeric column, MySQL automatically adds the UNSIGNED attribute to the column.

Unsigned type can be used to permit only nonnegative numbers in a column or when you need a larger upper numeric range for the column

详情:http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html

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KEY Username (username) ?

是用户名列用户名之后的索引名

详情:http://dev.mysql.com/doc/refman/5.0/en/create-table.html