Auto Generated Identity column to User generated Identity Column

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Hi,

Which is the right way to set identity column?

Way 1:

Auto-generated identity

SQL

identity(1,1)

Way 2:

Manual generated Identity

SQL

select @Identity = max(isnull(pkColumn,0))+1 from table

Please clarify..
Regards,
SJ

Posted 7-Jun-13 1:27am

codeninja-C#

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2 solutions

Solution 1

Way 1:
[Id] [int] IDENTITY(1,1) NOT NULL

Posted 7-Jun-13 1:30am

SagarRS

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Maciej Los · Accepted Answer · 2013-06-07T02:06:00

First way is right way, because it guarantee data integrity!
Read this: IDENTITY()[^] to get explanation ;)

Second way is pseudo-identity and does NOT guarantee unical numbers and data integrity. Why?
Imagine this situation: Your MAX(PK)=500. You have added 1 record, so your "identity" is equal: MAX+1=501. Delete last record and add it again. What number ("identity") you'll get? What happend if in other table exists foreign key with 501? You'll lose data integrity.