Logic in a default constraint?

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Logic in a default constraint?

Khades

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Points: 2067
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March 10, 2015 at 6:36 pm

#301945

We have just a regular identity column present. The requirement is to add another column which needs to have the value of 'A' + DATE of when it was inserted + ID
Something like this:
CREATE TABLE #Temp(ID INT IDENTITY(1,1), Name VARCHAR(50), CalculatedColumn VARCHAR(30))
ALTER TABLE #Temp
ADD CONSTRAINT DF_CC DEFAULT 'A' + CONVERT(VARCHAR(10), GETDATE(), 112) + CONVERT(VARCHAR(10), ID, 0)
FOR CalculatedColumn
Can't use another column in a default apparently. It will also not let me to do this with a persisted computed column since I'm using Varchar. Is there any other way to do this besides making the processes that insert into this table do the logic?

Viewing 6 posts - 1 through 5 (of 5 total)

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tomaz.kastrun SSCrazy Points: 2141 More actions · Answer 1

Hi,

you can use this:

create table #temp

(

id int identity(1,1)

,name varchar(50)

,calc as char(65) + convert(varchar(10), getdate(),112) + convert(varchar(20), id, 0)

)

and it should work.

Best, Tomaž

Tomaž Kaštrun | twitter: @tomaz_tsql | Github: https://github.com/tomaztk | blog: https://tomaztsql.wordpress.com/

Khades SSCrazy Points: 2067 More actions · Answer 2

tomaz.kastrun (3/11/2015)
Hi,
you can use this:
create table #temp
(
id int identity(1,1)
,name varchar(50)
,calc as char(65) + convert(varchar(10), getdate(),112) + convert(varchar(20), id, 0)
)
and it should work.
Best, Tomaž

The problem with this is that every time you do a select it will have a different value. We need the date to be the time when the record was inserted and not when you select it.

Lowell SSC Guru Points: 323518 More actions · Answer 3

Khades i tried with a user defined function as the default as wlel, doesn't work;

i think you're stuck with adding an trigger for insert in order to get your default value.

Lowell

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Khades SSCrazy Points: 2067 More actions · Answer 4

Lowell (3/11/2015)
Khades i tried with a user defined function as the default as wlel, doesn't work;
i think you're stuck with adding an trigger for insert in order to get your default value.

Thanks, that's actually a pretty good idea.

I'm going to speak with architecture to see if it's a good idea for us to also add a create_date column with a getdate() default, and the computed column just concatenates the two. If not, I'll go with the trigger.

Dwain Camps SSC Guru Points: 86948 More actions · Answer 5

Why can't you do this?

CREATE TABLE #Temp

(

ID INT IDENTITY(1,1)

,Name VARCHAR(50)

,InsertedDT DATETIME DEFAULT(GETDATE())

,CalculatedColumn AS ('A' + CONVERT(VARCHAR(10), InsertedDT, 112) + RIGHT(1000000000+ID, 9))

);

INSERT INTO #Temp (Name)

SELECT 'ABC';

SELECT *

FROM #Temp;

GO

DROP TABLE #Temp;

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