--A. 測試 datetime 精度問題
DECLARE @t TABLE(date char(21))
INSERT @t SELECT '1900-1-1 00:00:00.000'
INSERT @t SELECT '1900-1-1 00:00:00.001'
INSERT @t SELECT '1900-1-1 00:00:00.009'
INSERT @t SELECT '1900-1-1 00:00:00.002'
INSERT @t SELECT '1900-1-1 00:00:00.003'
INSERT @t SELECT '1900-1-1 00:00:00.004'
INSERT @t SELECT '1900-1-1 00:00:00.005'
INSERT @t SELECT '1900-1-1 00:00:00.006'
INSERT @t SELECT '1900-1-1 00:00:00.007'
INSERT @t SELECT '1900-1-1 00:00:00.008'
SELECT date,轉換后的日期=CAST(date as datetime) FROM @t

/*--結果

date                  轉換后的日期
--------------------- --------------------------
1900-1-1 00:00:00.000 1900-01-01 00:00:00.000
1900-1-1 00:00:00.001 1900-01-01 00:00:00.000
1900-1-1 00:00:00.009 1900-01-01 00:00:00.010
1900-1-1 00:00:00.002 1900-01-01 00:00:00.003
1900-1-1 00:00:00.003 1900-01-01 00:00:00.003
1900-1-1 00:00:00.004 1900-01-01 00:00:00.003
1900-1-1 00:00:00.005 1900-01-01 00:00:00.007
1900-1-1 00:00:00.006 1900-01-01 00:00:00.007
1900-1-1 00:00:00.007 1900-01-01 00:00:00.007
1900-1-1 00:00:00.008 1900-01-01 00:00:00.007

（所影響的行數為 10 行）
--*/
GO

--B. 對于 datetime 類型的純日期和時間的十六進制表示
DECLARE @dt datetime

--單純的日期
SET @dt='1900-1-2'
SELECT CAST(@dt as binary(8))
--結果: 0x0000000100000000

--單純的時間
SET @dt='00:00:01'
SELECT CAST(@dt as binary(8))
--結果: 0x000000000000012C
GO

--C. 對于 smalldatetime 類型的純日期和時間的十六進制表示
DECLARE @dt smalldatetime

--單純的日期
SET @dt='1900-1-2'
SELECT CAST(@dt as binary(4))
--結果: 0x00010000

--單純的時間
SET @dt='00:10'
SELECT CAST(@dt as binary(4))
--結果: 0x0000000A