=====================
表名为：tableName
时间字段名为：theDate
=====================
datePart函数

日期部分	缩写
year	yy, yyyy
quarter	qq, q
month	mm, m
dayofyear	dy, y
day	dd, d
week	wk, ww
weekday	dw
Hour	hh
minute	mi, n
second	ss, s
millisecond	ms

查询本日的记录
select * from tableName where DATEPART(dd, theDate) = DATEPART(dd, GETDATE()) and DATEPART(mm, theDate) = DATEPART(mm, GETDATE()) and DATEPART(yy, theDate) = DATEPART(yy, GETDATE())

查询本周的记录
select * from tableName where DATEPART(wk, theDate) = DATEPART(wk, GETDATE()) and DATEPART(yy, theDate) = DATEPART(yy, GETDATE())

查询本月的记录
select * from tableName where DATEPART(mm, theDate) = DATEPART(mm, GETDATE()) and DATEPART(yy, theDate) = DATEPART(yy, GETDATE())

查询本季的记录
select * from tableName where DATEPART(qq, theDate) = DATEPART(qq, GETDATE()) and DATEPART(yy, theDate) = DATEPART(yy, GETDATE())

查询本年的记录
select * from tableName where DATEPART(yy, theDate) = DATEPART(yy, GETDATE())


其中:GETDATE()是获得系统时间的函数。 

--------------------------------------------------------------------------------------------------------------------------------------------------
datediff函数

日期部分	缩写
year	yy, yyyy
quarter	qq, q
Month	mm, m
dayofyear	dy, y
Day	dd, d
Week	wk, ww
Hour	hh
minute	mi, n
second	ss, s
millisecond	ms

查询本日的记录
select count(*) from tableName where (DATEDIFF(dd, theDate, GETDATE()) = 0)
查询本周的记录
select count(*) from tableName where (DATEDIFF(wk, theDate, GETDATE()) = 0)
查询本月的记录
select count(*) from tableName where (DATEDIFF(mm, theDate, GETDATE()) = 0)
查询本季的记录
select count(*) from tableName where (DATEDIFF(qq, theDate, GETDATE()) = 0)
查询本年的记录
select count(*) from tableName where (DATEDIFF(yy, theDate, GETDATE()) = 0)

原始文章：http://blog.csdn.net/coolwzjcool/archive/2007/08/25/1758470.aspx