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MYSQL很好的SQL语句
MYSQL-
1.将查询结果中的0/1分别显示女/男SELECT CASE sexWHEN 1 THEN '男'WHEN 0 THEN '女'ELSE '不确定'ENDFROM carsystem.user2.删除表的一列alter table TEST_USER drop column age3.只更新当天登陆的民警的退出时间Update policemenlogin set quitdate=now() WHERE policemenId='p4' and to_days(logindate)8to_days(now())4.查过去24小时之内的数据（一下内容参见另一篇文章：2013.10.13 事务特性、MYSQL 触发器、存储过程、函数）核心：checkDate >DATE_ADD(now(), INTERVAL -1 DAY)String sql = "select * from records where vehicleId='" + vehicleId+ "' and checkDate >DATE_ADD(now(), INTERVAL -1 DAY)"+ " order by checkDate DESC";DATE_ADD(now(),INTERVAL -1 DAY);系统函数,指当前时间减去1天，即过去24小时时间段内5.按天数统计数据数量SELECT COUNT(*),records.checkdate FROM records GROUP BY TO_DAYS(records.checkdate);6.按月份统计数据数量SELECT COUNT(*),records.checkdate FROM records GROUP BY MONTH(records.checkdate);7.获取当天数据select * from policemenlogin where DATE_FORMAT(logindate,'%Y-%m-%d')=CURDATE();//取当天数据8.按月份分组SELECT DATE_FORMAT(time,'%Y%m') t,COUNT(*) '数量' FROM `user` GROUP BY PERIOD_DIFF( t,'200001');PERIOD_DIFF( t,'200001');//返回2000年01月到t时间的总月份数
