Thursday, September 13, 2007

Do You Know How Between Works With Dates?

Do you use between to return data that has dates? Do you know that between will get everything since midnight from the first criteria and up to midnight exactly from the second criteria. If you do BETWEEN 2006-10-01 AND 2006-10-02 then all the values that are greater or equal than 2006-10-01 and less or equal to 2006-10-02 will be returned. So no values after 2006-10-02 midnight will be returned.

Let's test this out, first let's create this table

CREATE TABLE SomeDates (DateColumn DATETIME)

Insert 2 values
INSERT INTO SomeDates VALUES('2006-10-02 00:00:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:00:00.000')

Return everything between '2006-10-01' and '2006-10-02'
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061002'
ORDER BY DateColumn
This works without a problem

Let's add some more dates including the time portion
INSERT INTO SomeDates VALUES('2006-10-02 00:01:00.000')
INSERT INTO SomeDates VALUES('2006-10-02 00:00:59.000')
INSERT INTO SomeDates VALUES('2006-10-02 00:00:01.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:01:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:12:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 23:00:00.000')


Return everything between '2006-10-01' and '2006-10-02'
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061002'
ORDER BY DateColumn
Here is where it goes wrong; for 2006-10-02 only the midnight value is returned the other ones are ignored


Now if we change 2006-10-02 to 2006-10-03 we get what we want
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061003'
ORDER BY DateColumn

Now insert a value for 2006-10-03 (midnight)

INSERT INTO SomeDates VALUES('2006-10-03 00:00:00.000')

Run the query again
SELECT *
FROM SomeDates
WHERE DateColumn BETWEEN '20061001' AND '20061003'
ORDER BY DateColumn

We get back 2006-10-03 00:00:00.000; between will return the date if it is exactly midnight

If you use >= and < then you get exactly what you need
SELECT *
FROM SomeDates
WHERE DateColumn >= '20061001' AND DateColumn < '20061003'
ORDER BY DateColumn

--Clean up
DROP TABLE SomeDates


So be careful when using between because you might get back rows that you did not expect to get back and it might mess up your reporting if you do counts or sums

2 comments:

Eric Vitiello said...

To return proper results using BETWEEN, you should make sure to include the times in the query:

WHERE time_field IS BETWEEN '10-12-2007 12:00:00.000' AND '10-13-2007 11:59:59.999'

SQL said...

Eric, that will fail since datetime precision is 300th of a second

run this

CREATE TABLE SomeDates (DateColumn DATETIME)


INSERT INTO SomeDates VALUES('2006-10-02 00:00:00.000')
INSERT INTO SomeDates VALUES('2006-10-01 00:00:00.000')

SELECT *
FROm SomeDates
WHERE DateColumn BETWEEN '2006-10-01 00:00:00.000' AND '2006-10-01 23:59:59.999'


you need to do this

SELECT *
FROm SomeDates
WHERE DateColumn BETWEEN '2006-10-01 00:00:00.000' AND '2006-10-01 23:59:59.997'

And with the nano second precision that might fail to. That is why >= and < is always the better way