SUBSTRING('sde123-TRE',3,6)="e123-T"（从给定字符串的指定位置开始，取指定长度的字符）
DATEPART() 返回给定日期的指定部分
DATEPART(yy,'2003-12-27')=2003-------year/yyyy
同义函数：year('2003-12-27')=2003
DATEPART(mm,'2003-12-27')=12----month/m
同义函数：month('2003-12-27')=12
DATEPART(dd,'2003-12-27')=27----day/d
同义函数：day('2003-12-27')=27
DATEPART(dw,'2003-12-27')=7-----weekday(该日是一周的第七天，即星期六)
DATEPART(hh,'13:55:34')=13------hour
DATEPART(mi,'13:55:34')=55------minute
DATEPART(ss,'13:55:34')=34------second
SELECT
substring(beginTime,12,2) hour, DATEPART(hh, beginTime)
FROM
dbo.LOG_INFO where logType=1 and subsystem =7 and beginTime>'2013-02-01' and beginTime < '2013-05-01'
