Try it out..

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Try it out..

Ujar

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August 3, 2010 at 8:31 pm

#222112

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UMG Developer SSChampion Points: 13482 More actions · Answer 1

Nice question thanks!

Though instead of your explanation I mights say "While ISNULL returns that value with the type of the first parameter COALESCE returns the value with they type of the actual value being returned."

So it would be perfectly reasonable for a single COALESCE statement to return 5 or more different types depending on the inputs. (Well maybe not reasonable, but certainly possible.)

On the other hand a given ISNULL statement will always return the same type.

VM-723206 SSCrazy Points: 2964 More actions · Answer 2

VM-723206

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Points: 2964

August 4, 2010 at 1:27 am

#1201904

Nice Question.

tommyh SSCertifiable Points: 6302 More actions · Answer 3

Good question. However an option with "GIVEN STRING IS NULL, GIV" would have been good. As the question stands its rather easy to guess. An inverted correct answer would have made it harder for people guessing (like me :-D).

arun1_m1 SSCommitted Points: 1949 More actions · Answer 4

Good Question. Thought both would truncate to 'GIV' and 'GIV'. Should have been more thoughtful.:-)

Duncan Pryde SSCertifiable Points: 7956 More actions · Answer 5

Good question - it was obvious immediately what was being asked, which is always nice (I always have a problem with obscure/trick questions!).

Also, it's nice to be reminded of these things (I rarely use ISNULL - perhaps this is why.)

Duncan

Dennissinned Ten Centuries Points: 1318 More actions · Answer 6

Dennissinned

Ten Centuries

Points: 1318

August 4, 2010 at 5:44 am

#1201996

Good question - Learned something new.

Daniel Bowlin SSC-Dedicated Points: 34566 More actions · Answer 7

Great question. I love QoTDs like this. They make me think and maybe read a little to make sure I understand something. Best of all QoTD is definitely making me better at all aspects of SQL Server. It is a great way to start the day and continually test and expand my knowledge.

Bradley Deem SSCrazy Points: 2565 More actions · Answer 8

UMG Developer (8/3/2010)
So it would be perfectly reasonable for a single COALESCE statement to return 5 or more different types depending on the inputs. (Well maybe not reasonable, but certainly possible.)

Actually, with Coalesce it comes down to the expression with the highest data type precedence being returned, thus exactly 1 predictable type will be returned. Consider the following which results in an error.

DECLARE @STR int

SET @STR=NULL

SELECT COALESCE(@STR,'GIVEN STRING IS NULL',CAST(1 AS DATETIME))

Conversion failed when converting date and/or time from character string.

In terms of precedence, Datetime > Int > String, thus the int can be cast into a DateTime, but the String cannot, hence the error.

UMG Developer SSChampion Points: 13482 More actions · Answer 9

Bradley Deem (8/4/2010)[hrActually, with Coalesce it comes down to the expression with the highest data type precedence being returned, thus exactly 1 predictable type will be returned. Consider the following which results in an error.

Argh... Thanks for the correction, I knew that but for whatever reason wasn't thinking straight...

SQLRNNR SSC Guru Points: 281334 More actions · Answer 10

Thanks for the question.

Jason...AKA CirqueDeSQLeil
_______________________________________________
I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
Posting Performance Based Questions - Gail Shaw[/url]
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adorable_412in Say Hey Kid Points: 711 More actions · Answer 11

adorable_412in

Say Hey Kid

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August 4, 2010 at 10:58 am

#1202217

Good Question.:-)

ziangij SSCertifiable Points: 7986 More actions · Answer 12

ziangij

SSCertifiable

Points: 7986

August 4, 2010 at 10:32 pm

#1202481

nice info about isnull and coalesce... thanks 🙂

Andre Guerreiro SSCertifiable Points: 7319 More actions · Answer 13

Very nice question.

Fortunately for me, I've come to know the differences of both functions while studying for the MCTS exam.

The best of all are these discussions about the question of the day.

You always get to learn something new and read the opinions of more qualified professionals than me. 🙂

Best regards,

Andre Guerreiro Neto

Database Analyst
http://www.softplan.com.br
MCITPx1/MCTSx2/MCSE/MCSA

Gopi S Ten Centuries Points: 1091 More actions · Answer 14

Hi,

Thanks for posting this. I have few clarification on COALESCE result type and i am confused the type conversion.

Consider the case below.

--Case 1

DECLARE @STR int

SET @STR=NULL

SELECT COALESCE(@STR,null,CAST('2010-05-05' AS DATETIME))

Result: 2010-05-05 00:00:00.000

--Case 2

DECLARE @STR2 int

SET @STR2=NULL

SELECT COALESCE(@STR2,null,CAST('ABCD' AS varchar(10)))

Result:

Error: Msg 245, Level 16, State 1, Line 9

Conversion failed when converting the varchar value 'ABCD' to data type int.

--Case 3

DECLARE @STR2 int

SET @STR2=NULL

SELECT COALESCE(@STR2,null,CAST('2222' AS varchar(10)))

Result: 2222

In case1, @STR is int type, but expression 2 in COALESCE is datetime. But i except the output to be 40301 which is the int value for date 2010-05-05 when following rule on case2 and case 3?

How case1 is evaluated?

Also what exactly mean by "1. Data type determination of the resulting expression - ISNULL uses the first parameter type, COALESCE follows the CASE expression rules and returns type of value with highest precedence"

Thanks in advance

Gopi