Using case in updating column

  • ok i have a table called "weights" that has following columns

    id shipweight1 shipweight2 shipweight3

    Right now i have the following query

    @id int,

    @weight int

    as

    if not exists(select id from weights where id = @id)

    begin

    insert into weights (id,shipweight1)

    values(@id,@weight)

    end

    else if *****

    So if the id does not exist in the table then it adds it and shipweight1

    Now for the else if .

    If the record does exist, i want to check if shipweight2 is null if it is i want to update that field if not i want to update shipweight3.

    If shipweight3 is not null i dont want it to update anything. Does this make since.

    Would i just have to do this

    else

    UPDATE weights

    SET shipweight2 = CASE WHEN shipweight2 is null THEN @weight ELSE shipweight2 END,

    shipweight3 = CASE WHEN shipweight2 is not null and shipweight3 is null THEN @weight else shipweight3

    thanks for the help

  • Very close. I would make some slight adjustments as follows:

    UPDATE dbo.weights

    SET

    shipweight2 = CASE WHEN shipweight2 IS NULL THEN @weight ELSE shipweight2 END,

    --CASE is just to doublecheck -- should always apply because of the WHERE conditions

    shipweight3 = CASE WHEN shipweight2 IS NOT NULL AND shipweight3 IS NULL THEN @weight ELSE shipweight3 END

    WHERE

    id = @id AND

    (shipweight2 IS NULL OR shipweight3 IS NULL)

    SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.

  • actually that wont work, if shipweight2 and shipweight3 are both null it will update them both. I dont want that

  • Maybe not that you need, but this works

    DECLARE

    @id int,

    @weight int,

    @Field varchar(12),

    @Result int

    -- Test values

    --SET @iD = 3

    --SET @weight = 28

    IF NOT EXISTS(SELECT id FROM [dbo].[weights] WHERE iD = @id)

    BEGIN

    INSERT INTO [dbo].[weights](id,shipweight1)

    VALUES(@id,@weight)

    END

    ELSE BEGIN

    SELECT @Result = shipweight2 FROM [dbo].[weights] WHERE iD = @iD

    SELECT @Field =

    CASE

    WHEN @Result <> 0 THEN 'shipweight3'

    ELSE 'shipweight2'

    END

    IF @Field = 'shipweight2' BEGIN

    UPDATE [dbo].[weights]

    SET shipweight2 = @weight

    WHERE iD = @iD

    END

    ELSE BEGIN

    -- check first if is null, for not overwrite

    SELECT @Result = shipweight3 FROM [dbo].[weights] WHERE iD = @iD

    IF @Result is null BEGIN

    UPDATE [dbo].[weights]

    SETshipweight3 = @weight

    WHERE iD = @iD

    END

    END

    END

    -- SELECT * FROM [dbo].[weights] WHERE iD = @iD

  • Is there some reason you can't or won't use a MERGE for this?

    CREATE TABLE #Weights

    (id INT, shipweight1 DECIMAL(5,2)

    ,shipweight2 DECIMAL(5,2), shipweight3 DECIMAL(5,2))

    INSERT INTO #Weights (id, shipweight1, shipweight2)

    SELECT 1, 1.1, NULL

    UNION ALL SELECT 2, 3.1, 2.3

    SELECT * FROM #Weights

    ;WITH SampleData (id, [weight]) AS (

    SELECT 1, 4.4

    UNION ALL SELECT 2, 5.5

    UNION ALL SELECT 3, 6.6)

    MERGE #Weights t

    USING SampleData s

    ON t.id = s.id

    WHEN MATCHED THEN

    UPDATE SET shipweight3 = CASE WHEN shipweight2 IS NULL THEN NULL ELSE weight END

    ,shipweight2 = CASE WHEN shipweight2 IS NULL THEN [weight] ELSE shipweight2 END

    WHEN NOT MATCHED THEN

    INSERT (id, shipweight1)

    VALUES (s.id, weight);

    SELECT * FROM #Weights

    DROP TABLE #Weights

    Looks a bit cleaner to me.


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  • Michael T2 (10/5/2012)


    actually that wont work, if shipweight2 and shipweight3 are both null it will update them both. I dont want that

    No, if both are NULL, only shipweight2 will UPDATE, because I left your condition on the second CASE that verifies that shipweight2 is not null.

    SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.

  • oh right sorry about that.

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