How to Deduplicate an id column by adding an overflow column? - sql

Question

Alright guys I need some help! I am need to duplicate the ID Column and I'm having trouble with adding a column without loosing important data.
Is there a way to make an "overflow column" that would take the secondary [tags] and put them into a new column?
Here is the example:
**UniqueId** **Age** **Zip*** **Tag**
1 20 11111 yellow
2 25 33333 blue
2 25 33333 black
3 30 44444 purple
3 30 44444 pink
3 30 44444 white
This is what i want the output to look like
**UniqueId** **Age** **Zip*** **Tag1** **Tag2** **Tag3**
1 20 11111 yellow NULL NULL
2 25 33333 blue black NULL
3 30 44444 purple pink white
Your help would be greatly appreciated!!!

Answer 1

If you now the maximum number of tags, you can use pivot or conditional aggregation:
select t.uniqueid, t.age, t.zip,
max(case when seqnum = 1 then tag end) as tag_1,
max(case when seqnum = 2 then tag end) as tag_2,
max(case when seqnum = 3 then tag end) as tag_2
from (select t.*,
row_number() over (partition by uniqueid order by (select null)) as seqnum
from t
) t
group by t.uniqueid, t.age, t.zip;

Answer 2

Though I tend to prefer conditional aggregations as Gordon illustrated... they offer a bit more flexibilty.
You can do a simple PIVOT
Example
Select *
From (
Select UniqueID
,Age
,Zip
,Tag
,Col = concat('Tag',Row_Number() over (Partition By UniqueId order by Tag) )
From YourTable
) A
Pivot (Max(Tag) for Col in ([Tag1],[Tag2],[Tag3],[Tag4]) ) p
Returns
UniqueID Age Zip Tag1 Tag2 Tag3 Tag4
1 20 11111 yellow NULL NULL NULL
2 25 33333 black blue NULL NULL
3 30 44444 pink purple white NULL

Answer 3

attention: Do not store the age as an int number! Rather store a DOB and compute the age...
This is not a real answer to your question, but the thing you should rather do:
To be honest: Your question can be solved (and there are good answers already), but you should not do this.
Whenever you feel the need to add numbers to a field's name (Tag1, Tag2...) the design will be wrong (almost ever). Push these values into a related side table (just the Id and the tag), remove the column from your original table and place a foreign key pointing to the new table. Now you can join these values whenever you need them. PIVOT (or conditional aggregation) is for output only...
This is completely untested, so be careful with your data (backup!), but something along these lines should work:
CREATE TABLE TagTable (ID INT IDENTITY
,FKOriginal INT NOT NULL CONSTRAINT FK_TagTable_OriginalTable FOREIGN KEY REFERENCES OriginalTable(UniqueId)
,Tag VARCHAR(100) NOT NULL);
--an index to support the fk
CREATE NONCLUSTERED INDEX IX_TagTable_FKOriginal ON TagTable(FKOriginal);
GO
--shift the existing data
INSERT INTO TagTable --you might use DISTINCT...
SELECT UniqueId,Tag
FROM OriginalTable;
GO
--delete duplicated rows
WITH cte AS
(
SELECT *
,ROW_NUMBER() OVER(PARTITION BY UniqueId ORDER BY UniqueId) AS RowId --Find a better sort column if needed
FROM OriginalTable
)
DELETE FROM cte
WHERE RowId>1; --Only the first remains
GO
--throw away the tag column in the original table
ALTER TABLE OriginalTable DROP COLUMN Tag;
GO
--See the result via JOIN-Select
SELECT *
FROM OriginalTable AS o
INNER JOIN TagTable AS t ON o.UniqueId=t.FKOriginal;
If you need these pivoted columns, you can use the approaches provided in other answers with the final SELECT too.