先看下边的SQL 语句
CREATE TABLE #DateTest(
Id INT,
SampleDate DATETIME
)
INSERT INTO #DateTest VALUES(1,‘1 jan 2010 10:30‘)
INSERT INTO #DateTest VALUES(2,‘2 jan 2010 23:59‘)
INSERT INTO #DateTest VALUES(3,‘3 jan 2010 12:34‘)
INSERT INTO #DateTest VALUES(4,‘3 jan 2010 12:56‘)
INSERT INTO #DateTest VALUES(5,‘4 jan 2010‘)
INSERT INTO #DateTest VALUES(6,‘4 jan 2010 00:00‘)
INSERT INTO #DateTest VALUES(7,‘4 jan 2010 13:31‘)
INSERT INTO #DateTest VALUES(8,‘4 jan 2010 00:10‘)
INSERT INTO #DateTest VALUES(9,‘5 jan 2010 12:01‘)
DECLARE @DATE1 DATETIME
DECLARE @DATE2 DATETIME
SELECT @DATE1 = ‘2 jan 2010‘
SELECT @DATE2 = ‘4 jan 2010‘
SELECT Id
FROM #DateTest
WHERE SampleDate BETWEEN @DATE1 AND @DATE2
DROP TABLE #DateTest
查询语句查询的是‘2010-01-02 00:00:00.000‘到‘2010-01-04 00:00:00.000‘的时间,所以查询结果为2,3,4,5,6。
再执行如下的SQL 语句:
CREATE TABLE #DateTest(
Id INT,
SampleDate DATETIME
)
INSERT INTO #DateTest VALUES(1,‘2010-01-01T10:30:21.000‘)
INSERT INTO #DateTest VALUES(2,‘2010-01-01T23:59:59.999‘)
INSERT INTO #DateTest VALUES(3,‘2010-01-02T12:56:00.000‘)
INSERT INTO #DateTest VALUES(4,‘2010-01-02T23:59:59.998‘)
INSERT INTO #DateTest VALUES(5,‘2010-01-03T00:00:00.000‘)
INSERT INTO #DateTest VALUES(6,‘2010-01-03T13:31:00.000‘)
INSERT INTO #DateTest VALUES(7,‘2010-01-04T00:00:00.001‘)
INSERT INTO #DateTest VALUES(8,‘2010-01-04T00:00:00.002‘)
INSERT INTO #DateTest VALUES(9,‘2010-01-05T12:01:00.002‘)
DECLARE @DATE1 DATETIME
DECLARE @DATE2 DATETIME
SELECT @DATE1 = ‘2 jan 2010‘
SELECT @DATE2 = ‘4 jan 2010‘
SELECT *
FROM #DateTest
WHERE SampleDate BETWEEN @DATE1 AND @DATE2
DROP TABLE #DateTest
查询结果为:
Id SampleDate
----------- -----------------------
2 2010-01-02 00:00:00.000
3 2010-01-02 12:56:00.000
4 2010-01-02 23:59:59.997
5 2010-01-03 00:00:00.000
6 2010-01-03 13:31:00.000
7 2010-01-04 00:00:00.000
在执行结果中,ID为2的日期变成2010-01-02 00:00:00.000.这是为什么呢?
因为,在SQL SERVER中DATETIME表示的时间为00:00:00到23:59:59.997,它的时间精度为1/300秒,在使用时会舍入到舍入到 .000、.003 或 .007 秒三个增量。如下表是DATETIME秒的小数部分精度的舍入。
用户指定的值 |
系统存储的值 |
01/01/98 23:59:59.999 |
1998-01-02 00:00:00.000 |
01/01/98 23:59:59.995 01/01/98 23:59:59.996 01/01/98 23:59:59.997 01/01/98 23:59:59.998 |
1998-01-01 23:59:59.997 |
01/01/98 23:59:59.992 01/01/98 23:59:59.993 01/01/98 23:59:59.994 |
1998-01-01 23:59:59.993 |
01/01/98 23:59:59.990 |
根据这一规则,在上边的SQL语句中,实际插入表中的数据为:
Id SampleDate
----------- -----------------------
1 2010-01-01 10:30:21.000
2 2010-01-02 00:00:00.000
3 2010-01-02 12:56:00.000
4 2010-01-02 23:59:59.997
5 2010-01-03 00:00:00.000
6 2010-01-03 13:31:00.000
7 2010-01-04 00:00:00.000
8 2010-01-04 00:00:00.003
9 2010-01-05 12:01:00.003
在查询某一天当中的数据时,如果查询条件为BETWEEN ‘2010-01-02T00:00:00.000‘
AND ‘2010-01-02T23:59:59.999‘,实际查询的是‘2010-01-02T00:00:00.000‘
到‘2010-01-03T00:00:00.000‘之间的数据。
例子如,将上边的SQ语句的查询条件更改为:
SELECT @DATE1 = ‘2010-01-02T00:00:00.000‘
SELECT @DATE2 = ‘2010-01-02T23:59:59.999‘
其执行结果:
Id SampleDate
----------- -----------------------
2 2010-01-02 00:00:00.000
3 2010-01-02 12:56:00.000
4 2010-01-02 23:59:59.997
5 2010-01-03 00:00:00.000
所以,在查询某一天的数据时,查询条件应为:BETWEEN ‘2010-01-02T00:00:00.000‘
AND ‘2010-01-02T23:59:59.998‘。
更改查询条件,重新执行查询:
SELECT @DATE1 = ‘2010-01-02T00:00:00.000‘
SELECT @DATE2 = ‘2010-01-02T23:59:59.998‘
其执行结果为:
Id SampleDate
----------- -----------------------
2 2010-01-02 00:00:00.000
3 2010-01-02 12:56:00.000
4 2010-01-02 23:59:59.997
在SQL SERVER 2008中新增了Datetime2类型,可以提供更高的时间精度,且可以自定义时间精度,以后可以使用这种数据类型。