Changing Identity Columns

  • Comments posted to this topic are about the item Changing Identity Columns

    Kenneth FisherI was once offered a wizards hat but it got in the way of my dunce cap.--------------------------------------------------------------------------------For better, quicker answers on T-SQL questions, click on the following... http://www.sqlservercentral.com/articles/Best+Practices/61537/[/url]For better answers on performance questions, click on the following... http://www.sqlservercentral.com/articles/SQLServerCentral/66909/[/url]Link to my Blog Post --> www.SQLStudies.com[/url]

  • Good topic for a follow-up QOD (hope I don't steal any thunder here):

    If the code presented had one more statement amnd asked for the max(Ident)...

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('xyz') -- <== Added to original

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    INSERT INTO IdentTest VALUES ('abc')

    SELECT max(Ident) FROM IdentTest

    What would be the output?

    Wouldn't it be the same (100)?

    If not, WHY NOT? (hard to make a QOD an essay question, but if you got this far, give it a shot).

  • Very nice question indeed. Guess what sould be the output of the last select statement, If I add a TRUNCATE statement in the code as well:

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('abc')

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    INSERT INTO IdentTest VALUES ('abc')

    TRUNCATE TABLE identTest

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest

    ~ Lokesh Vij


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  • john.arnott (10/21/2012)


    Good topic for a follow-up QOD (hope I don't steal any thunder here):

    If the code presented had one more statement amnd asked for the max(Ident)...

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('xyz') -- <== Added to original

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    INSERT INTO IdentTest VALUES ('abc')

    SELECT max(Ident) FROM IdentTest

    What would be the output?

    Wouldn't it be the same (100)?

    If not, WHY NOT? (hard to make a QOD an essay question, but if you got this far, give it a shot).

    Very interesting. It kept me thinking....if there were more than 100 records in the table before Identity reseed command is executed...we have duplicate identity values 🙂

    ~ Lokesh Vij


    Guidelines for quicker answers on T-SQL question[/url]
    Guidelines for answers on Performance questions

    Link to my Blog Post --> www.SQLPathy.com[/url]

    Follow me @Twitter

  • Intersting thread:)

  • nice question to start on Monday with +1 :-):-P

    _______________________________________________________________
    To get quick answer follow this link:
    http://www.sqlservercentral.com/articles/Best+Practices/61537/

  • in this case the max ident value would be 101 as with first insert statement the value of ident was 100 and with another insert statement the ident value would be 101 and max from 101 and 100 is 101 so 101 is the max value..

    hope its clear to you

    _______________________________________________________________
    To get quick answer follow this link:
    http://www.sqlservercentral.com/articles/Best+Practices/61537/

  • Hi lokesh,

    as you TRUNCATE the table then identity will be reset to 1 and now the ident value after a insert statement will be 1..

    _______________________________________________________________
    To get quick answer follow this link:
    http://www.sqlservercentral.com/articles/Best+Practices/61537/

  • kapil_kk (10/22/2012)


    in this case the max ident value would be 101 as with first insert statement the value of ident was 100 and with another insert statement the ident value would be 101 and max from 101 and 100 is 101 so 101 is the max value..

    hope its clear to you

    Wrong!

    with first insert statement, identity value will be 1 and with second insert statement it will be 101.

    ~ Lokesh Vij


    Guidelines for quicker answers on T-SQL question[/url]
    Guidelines for answers on Performance questions

    Link to my Blog Post --> www.SQLPathy.com[/url]

    Follow me @Twitter

  • kapil_kk (10/22/2012)


    in this case the max ident value would be 101 as with first insert statement the value of ident was 100 and with another insert statement the ident value would be 101 and max from 101 and 100 is 101 so 101 is the max value..

    hope its clear to you

    Actually the question posted by John is little different. Execute the below code:

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('xyz') -- <== Added to original

    INSERT INTO IdentTest VALUES ('123') -- <== Added to original

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest -- <== (done away with max)

    Now the last select statement (done away with max statement intentionally), returns three values 1,2 and 101

    Why value 101?? Why not 100 or 102??

    ~ Lokesh Vij


    Guidelines for quicker answers on T-SQL question[/url]
    Guidelines for answers on Performance questions

    Link to my Blog Post --> www.SQLPathy.com[/url]

    Follow me @Twitter

  • Execute this code and you will get duplicate values in Identity values--

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('xyz') -- <== Added to original

    INSERT INTO IdentTest VALUES ('123') -- <== Added to original

    SELECT Ident FROM IdentTest

    -- Result 1,2

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    --Checking identity information: current identity value '2', current column value '100'.

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest

    --Result 1,2,101

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    --Checking identity information: current identity value '101', current column value '100'.

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest

    --Result 1,2,101,101

    Its intresting to know that functionality of identity is exploiting in this way

    _______________________________________________________________
    To get quick answer follow this link:
    http://www.sqlservercentral.com/articles/Best+Practices/61537/

  • kapil_kk (10/22/2012)


    Execute this code and you will get duplicate values in Identity values--

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('xyz') -- <== Added to original

    INSERT INTO IdentTest VALUES ('123') -- <== Added to original

    SELECT Ident FROM IdentTest

    -- Result 1,2

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    --Checking identity information: current identity value '2', current column value '100'.

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest

    --Result 1,2,101

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    --Checking identity information: current identity value '101', current column value '100'.

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest

    --Result 1,2,101,101

    Its intresting to know that functionality of identity is exploiting in this way

    Very true..that's what I was trying to point out:-)

    ~ Lokesh Vij


    Guidelines for quicker answers on T-SQL question[/url]
    Guidelines for answers on Performance questions

    Link to my Blog Post --> www.SQLPathy.com[/url]

    Follow me @Twitter

  • Lokesh Vij (10/22/2012)


    kapil_kk (10/22/2012)


    in this case the max ident value would be 101 as with first insert statement the value of ident was 100 and with another insert statement the ident value would be 101 and max from 101 and 100 is 101 so 101 is the max value..

    hope its clear to you

    Actually the question posted by John is little different. Execute the below code:

    CREATE TABLE IdentTest

    ( Ident INT NOT NULL IDENTITY (1,1)

    , varfield varchar(100)

    )

    INSERT INTO IdentTest VALUES ('xyz') -- <== Added to original

    INSERT INTO IdentTest VALUES ('123') -- <== Added to original

    DBCC CHECKIDENT ('IdentTest',RESEED,100)

    INSERT INTO IdentTest VALUES ('abc')

    SELECT Ident FROM IdentTest -- <== (done away with max)

    Now the last select statement (done away with max statement intentionally), returns three values 1,2 and 101

    Why value 101?? Why not 100 or 102??

    If data is present in the table before DBCC CHECKIDENT, the new identity value is the reseed value + current incremenet. In this case, 100 + 1 = 101.

    Anyway, nice question.

    Need an answer? No, you need a question
    My blog at https://sqlkover.com.
    MCSE Business Intelligence - Microsoft Data Platform MVP

  • Nice question.

  • Good question and thanks for an easy start to the week.

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