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kevin.l.williams
kevin.l.williams
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Thank you very much for this QOTD! I have been using COALESCE only when I was working with more than two values and was totally unaware of this behavior of ISNULL.



Tom Garth
Tom Garth
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Points: 1247 Visits: 1499
It happens every time. I hate being caught with a tricky one.

Good QD.

Tom Garth
Vertical Solutions

"There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." -- Will Rogers

Anipaul
Anipaul
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Good Question...



Bhuvnesh
Bhuvnesh
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Group: General Forum Members
Points: 5258 Visits: 4076
CREATE TABLE #TEST(A varchar,B varchar(30));
INSERT INTO #TEST(A) VALUES('A');
INSERT INTO #TEST(B) VALUES('Some text');
INSERT INTO #TEST(A) VALUES('B');
INSERT INTO #TEST(B) VALUES('Some more text');


SELECT COUNT(*)FROM #TEST GROUP BY LEN(ISNULL(B,A));
go
SELECT COUNT(*) from #TEST GROUP BY LEN(ISNULL(A,B));

Why above queries are giving differentt results?????????

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Bhuvnesh
Bhuvnesh
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Group: General Forum Members
Points: 5258 Visits: 4076
CREATE TABLE #TEST(A varchar,B varchar(30));
INSERT INTO #TEST(A) VALUES('A');
INSERT INTO #TEST(B) VALUES('Some text');
INSERT INTO #TEST(A) VALUES('B');
INSERT INTO #TEST(B) VALUES('Some more text');


SELECT COUNT(*)FROM #TEST GROUP BY LEN(ISNULL(B,A));
go
SELECT COUNT(*) from #TEST GROUP BY LEN(ISNULL(A,B));

Why above queries are giving differentt results?????????

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Ninja's_RGR'us
Ninja's_RGR'us
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Reread the question's explaination.

The first parameter in the isnull function determines what data type will be returned. Since one of the column is varchar(1), then when that column is in the parameter 1 spot, isnull returns a varchar(1)... truncating whatever is in column b... but it does not throw a truncation error nor warning for this.

That's why it's called a gotcha...
Bhuvnesh
Bhuvnesh
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hi,
if you see table creation syntax ,i m using A varchar(40) instead of A varchar

below queries resluts same but WHY????

CREATE
TABLE #TEST(A varchar(40),B varchar(30));
INSERT
INTO #TEST(A) VALUES('A');
INSERT
INTO #TEST(B) VALUES('Some text');
INSERT
INTO #TEST(A) VALUES('B');
INSERT
INTO #TEST(B) VALUES('Some more text');


SELECT
COUNT(*)FROM #TEST GROUP BY LEN(ISNULL(B,A));
go
SELECT
COUNT(*) from #TEST GROUP BY LEN(ISNULL(A,B));

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
GilaMonster
GilaMonster
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Group: General Forum Members
Points: 87527 Visits: 45272
Because none of the strings you have there are reaching the 30/40 character limit for the varchar. The ISNULL returns for the first query a data type of VARCHAR(30) and for the second query a VARCHAR(40)

The 'trick' to the original question was than in one case the ISNULL, because of the order of the parameters passed to it, returned a VARCHAR(1). LEN of a VARCHAR(1) can only be 1 or 0

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass


Bhuvnesh
Bhuvnesh
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Group: General Forum Members
Points: 5258 Visits: 4076
Thanks GILA...i got the point ....

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Preet_S
Preet_S
Old Hand
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Group: General Forum Members
Points: 346 Visits: 240
Questions like these should be worth more than 1 point!
Good 'trick' question!
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