Data Type and Length

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Data Type and Length

magasvs

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August 7, 2010 at 1:00 pm

#225814

Comments posted to this topic are about the item Data Type and Length

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Andre Guerreiro SSCertifiable Points: 7319 More actions · Answer 1

Thanks for question. I just lost one point. 😀

Now why in Heavens would there be two different behaviours for the same datatype?

Just to confuse people? Or is there a technical explanation for that?

Best regards,

Andre Guerreiro Neto

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

Oleg Netchaev SSCertifiable Points: 5276 More actions · Answer 2

codebyo (8/7/2010)
Now why in Heavens would there be two different behaviours for the same datatype?
Just to confuse people? Or is there a technical explanation for that?

This is a very good question, I really like it.

I think that this data type size behaviour is great. Since there is no way in SQL Server to punish the disobedient by, say, 12 lashes they deserve, this difference is actually a good way to teach them to never omit the size when declaring / converting variables. On the top of the 1 / 30 issue, there is another interesting twist to it: both ADODB and ADO.NET default the size of the varchar type procedure parameter to 50 if the size is not specified. The bottom line is that forgetting to specify the size is evil and should be avoided.

As far as a technical explanation is concerned, I believe that because the size is required, default values were provided by the parser team, and it probably just so happened that the declaration and conversion were written by different developers, that is all.

Oleg

UMG Developer SSChampion Points: 13482 More actions · Answer 3

Great question thanks!

This is a very good topic to cover, as I know a lot of developers don't understand the importance of specifying the size. (Good old VB "String" type.)

Andre Guerreiro SSCertifiable Points: 7319 More actions · Answer 4

Oleg Netchaev (8/7/2010)
I think that this data type size behaviour is great. Since there is no way in SQL Server to punish the disobedient by, say, 12 lashes they deserve, this difference is actually a good way to teach them to never omit the size when declaring / converting variables. On the top of the 1 / 30 issue, there is another interesting twist to it: both ADODB and ADO.NET default the size of the varchar type procedure parameter to 50 if the size is not specified. The bottom line is that forgetting to specify the size is evil and should be avoided.
As far as a technical explanation is concerned, I believe that because the size is required, default values were provided by the parser team, and it probably just so happened that the declaration and conversion were written by different developers, that is all.
Oleg

You're right. Trusting default behaviours should be avoided at all costs.

But 12 lashes is too soft. 😀

Best regards,

Andre Guerreiro Neto

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

SQLRNNR SSC Guru Points: 281334 More actions · Answer 5

Great question. As the others have said, this underlines the necessity of specifying the size of the datatype.

Jason...AKA CirqueDeSQLeil
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I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
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Bhuvnesh SSC Guru Points: 59351 More actions · Answer 6

30 is for char or varchar ?

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)

Hugo Kornelis SSC Guru Points: 64790 More actions · Answer 7

Good question! When I first saw it, I thought there would be a very high percentage of correct answers since the confusing default lengths for character strings have already been covered in a few recent QotD's. But the results say that at this time, only 53% of the respondents have given the right answer, so there is obviously still a lot of need to keep driving this point home. Good job, magasvs!

Bhuvnesh (8/9/2010)
30 is for char or varchar ?

Both, when used without length in a CONVERT() function call.

In a DECLARE, both char and varchar default to a length of 1.

Hugo Kornelis, SQL Server/Data Platform MVP (2006-2016)
Visit my SQL Server blog: https://sqlserverfast.com/blog/
SQL Server Execution Plan Reference: https://sqlserverfast.com/epr/

hrvoje.piasevoli Ten Centuries Points: 1377 More actions · Answer 8

Good question!

Hugo Kornelis (8/9/2010)
...I thought there would be a very high percentage of correct answers since the confusing default lengths for character strings have already been covered in a few recent QotD's.

I guess people don't go through discussions. (July, 19th QotD only asked for the implicit length of variable declaration while the CONVERT behavior was mentioned and explained in the discussion that followed.)

Regards,

Hrvoje

Hrvoje Piasevoli

paul.knibbs SSCoach Points: 15320 More actions · Answer 9

Completely forgot about the CONVERT when answering this, but probably would have got it wrong even if I'd taken it into account...didn't know about this default length behaviour!

Ameya- Ameyask SSC Veteran Points: 203 More actions · Answer 10

Very good question indeed. Takes back to basics 🙂

Dennissinned Ten Centuries Points: 1318 More actions · Answer 11

Dennissinned

Ten Centuries

Points: 1318

August 9, 2010 at 6:45 am

#1204122

Great Question. Thank you.

Kari Suresh Hall of Fame Points: 3712 More actions · Answer 12

[p]Good question. Thank you.[/p]

KSB
-----------------------------
Thousands of candles can be lit from a single candle, and the life of the candle will not be shortened. Knowledge and happiness never decreases by being shared.” - Buddha

Daniel Bowlin SSC-Dedicated Points: 34566 More actions · Answer 13

Curious, the difference in default behaviour between a DECLARE and a CONVERT.

I suppose this just puts another check mark in the Always Declare Everything column.

Sean Lange SSC Guru Points: 286590 More actions · Answer 14

Excellent question! I noticed the lack of defining the size and my initial response was 1;1 but since that was not a choice I figured there must be something in convert for default sizes. Had there been an answer of 1;1 I would have assumed that was the correct answer. 😉

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