MySQL - DATEDIFF(expr1,expr2)
[DATEDIFF(expr1,expr2)语法文档]
http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_datediff
[MySQL网站]
http://www.mysql.com/[MySQL相关论坛]
http://database.board.newsmth.net/, 不针对MySQL[MySQL语法]
CREATE TABLE, http://dev.mysql.com/doc/refman/5.1/zh/sql-syntax.html#create-table SHOW TABLE STATUS, http://dev.mysql.com/doc/refman/5.1/zh/sql-syntax.html#show-table-status
日期和时间类型概述文档, http://dev.mysql.com/doc/refman/5.1/zh/column-types.html#date-and-time-type-overview
JOIN语法文档, http://dev.mysql.com/doc/refman/5.1/zh/sql-syntax.html#join
