datetime 比较 mysql,mysql中datetime比较大小问题
select sum(studychj) as tofflinejzfrom afterline where checkflag=1 and studytype=1 and studybegin>='2010-01-01 00:00:00' and studyend<='2010-12-01 00:00:00' and username='01009'这么写不报错，但得出结果不准确方法...
