q

CREATE TABLE U(col1 INT);
INSERT INTO U VALUES(2);
INSERT INTO U VALUES(7);
INSERT INTO U VALUES(9);
CREATE TABLE V(col1 INT);
INSERT INTO V VALUES(3);
INSERT INTO V VALUES(7);
INSERT INTO V VALUES(NULL);
SELECT * FROM U WHERE
col1 NOT IN(SELECT col1 FROM V);
i expected it to return 2 and 9 but it returned nothing. can anyone explain?This is because of NULL value in the V table. Comparing to NULL, we don't
know whether the known values are equal or different, so we have to make an
agreement how to deal in such situations. In your case, you see the result.
If you want to get the values you are mentioning, change the query to
SELECT * FROM U WHERE
U.col1 NOT IN (SELECT V.col1 FROM V WHERE V.col1 IS NOT NULL);
Dejan Sarka, SQL Server MVP
Associate Mentor
www.SolidQualityLearning.com
"ichor" <ichor@.hotmail.com> wrote in message
news:OqZWh2FrFHA.2076@.TK2MSFTNGP14.phx.gbl...
> CREATE TABLE U(col1 INT);
> INSERT INTO U VALUES(2);
> INSERT INTO U VALUES(7);
> INSERT INTO U VALUES(9);
> CREATE TABLE V(col1 INT);
> INSERT INTO V VALUES(3);
> INSERT INTO V VALUES(7);
> INSERT INTO V VALUES(NULL);
>
> SELECT * FROM U WHERE
> col1 NOT IN(SELECT col1 FROM V);
> i expected it to return 2 and 9 but it returned nothing. can anyone
> explain?
>|||If you are using the NOT IN Opereator with a subquery and the subquery
contains any NULL values, the subquery will return NULL!. This can be
dangerous, and this is not the case if you use IN.
http://toponewithties.blogspot.com/...es.blogspot.com
"ichor" <ichor@.hotmail.com> wrote in message
news:OqZWh2FrFHA.2076@.TK2MSFTNGP14.phx.gbl...
> CREATE TABLE U(col1 INT);
> INSERT INTO U VALUES(2);
> INSERT INTO U VALUES(7);
> INSERT INTO U VALUES(9);
> CREATE TABLE V(col1 INT);
> INSERT INTO V VALUES(3);
> INSERT INTO V VALUES(7);
> INSERT INTO V VALUES(NULL);
>
> SELECT * FROM U WHERE
> col1 NOT IN(SELECT col1 FROM V);
> i expected it to return 2 and 9 but it returned nothing. can anyone
> explain?
>|||That exact example is given in Itzik Ben-Gan's T-SQL Black Belt column
this month in SQLMag (Don't Avoid the UNKNOWN
<http://www.windowsitpro.com/Article...47010.html?Ad=1> ).
If you want a fuller explanation, you should read his article.
*mike hodgson*
blog: http://sqlnerd.blogspot.com
Dejan Sarka wrote:

>This is because of NULL value in the V table. Comparing to NULL, we don't
>know whether the known values are equal or different, so we have to make an
>agreement how to deal in such situations. In your case, you see the result.
>If you want to get the values you are mentioning, change the query to
>SELECT * FROM U WHERE
> U.col1 NOT IN (SELECT V.col1 FROM V WHERE V.col1 IS NOT NULL);
>
>|||this is where i took the code from. i have subscribed to sqlmag but cant see
the entire article.
"Mike Hodgson" <mike.hodgson@.mallesons.nospam.com> wrote in message news:OA$
QFNGrFHA.3096@.TK2MSFTNGP15.phx.gbl...
That exact example is given in Itzik Ben-Gan's T-SQL Black Belt column this
month in SQLMag (Don't Avoid the UNKNOWN). If you want a fuller explanation
, you should read his article.
mike hodgson
blog: http://sqlnerd.blogspot.com
Dejan Sarka wrote:
This is because of NULL value in the V table. Comparing to NULL, we don't
know whether the known values are equal or different, so we have to make an
agreement how to deal in such situations. In your case, you see the result.
If you want to get the values you are mentioning, change the query to
SELECT * FROM U WHERE
U.col1 NOT IN (SELECT V.col1 FROM V WHERE V.col1 IS NOT NULL);