# Unpivoting Data

Unpivoting data is a very useful technique for normalizing denormalized tables. It refers to the process of transposing multiple columns across into rows in a single column. In other words, taking the data below:

`sales_year  first_quarter  second_quarter   third_quarter   fourth_quarter----------  -------------  --------------   -------------   --------------2006        211203.50      381594.95        439187.00       503155.802007        231205.10      451101.25        601209.40       531907.30`

and converting to look like this:

`sales_year   sales_quarter  sales_amount-----------  -------------  ------------2006         1              211203.502006         2              381594.952006         3              439187.002006         4              503155.802007         1              231205.102007         2              451101.252007         3              601209.402007         4              531907.30`

Here are different methods to achieve that:

`-- Create sample tableCREATE TABLE QuarterlySales ( sales_year INT PRIMARY KEY, first_quarter DECIMAL(10, 2), second_quarter DECIMAL(10, 2), third_quarter DECIMAL(10, 2), fourth_quarter DECIMAL(10, 2)); -- Insert dataINSERT INTO QuarterlySales VALUES(2006, 211203.50, 381594.95, 439187.00, 503155.80); INSERT INTO QuarterlySales VALUES(2007, 231205.10, 451101.25, 601209.40, 531907.30); -- Method 1) Using UNIONSELECT sales_year,        1 AS sales_quarter,        first_quarter AS sales_amountFROM QuarterlySalesUNION ALLSELECT sales_year, 2, second_quarterFROM QuarterlySalesUNION ALLSELECT sales_year, 3, third_quarterFROM QuarterlySales UNION ALLSELECT sales_year, 4, fourth_quarterFROM QuarterlySalesORDER BY sales_year, sales_quarter; -- Method 2) Using cross join with table with numbersSELECT sales_year,       qtr AS sales_quarter,       CASE qtr          WHEN 1 THEN first_quarter         WHEN 2 THEN second_quarter         WHEN 3 THEN third_quarter         WHEN 4 THEN fourth_quarter       END AS sales_amountFROM QuarterlySalesCROSS JOIN(SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4) AS Quarters(qtr)ORDER BY sales_year, sales_quarter; -- Method 3) Using the UNPIVOT operator in SQL Server 2005SELECT sales_year,       CASE sales_quarter         WHEN 'first_quarter' THEN 1         WHEN 'second_quarter' THEN 2         WHEN 'third_quarter' THEN 3         WHEN 'fourth_quarter' THEN 4       END AS sales_quarter,       sales_amount     FROM QuarterlySalesUNPIVOT(sales_amount FOR  sales_quarter IN  (first_quarter, second_quarter,   third_quarter, fourth_quarter)) AS UORDER BY sales_year, sales_quarter;`

It is good no note that unpivoting multiple columns (like amount1, date1, amount2, date2 to amount and date columns) is not supported by the SQL Server 2005 UNPIVOT operator. This can be achieved only by using the first two methods.

Using PIVOT and UNPIVOT
http://msdn2.microsoft.com/en-us/library/ms177410.aspx

Tags:
10 replies

Hi Plamen,
I solved the problem without tally table (number table).
I used GROUPING SET for copy some instance of data, then using ROW_NUMBER for sequence numbers then solving the unpivoting problem.

SELECT sales_year, rec_id AS sales_quarter,
CASE rec_id
WHEN 1 THEN first_quarter
WHEN 2 THEN second_quarter
WHEN 3 THEN third_quarter
WHEN 4 THEN fourth_quarter
END AS sales_amount
FROM
(
SELECT *, ROW_NUMBER() OVER(PARTITION BY sales_year ORDER BY (SELECT NULL)) AS rec_id
FROM QuarterlySales
GROUP BY GROUPING SETS
(
(sales_year, first_quarter, second_quarter, third_quarter, fourth_quarter),
(sales_year, first_quarter, second_quarter, third_quarter, fourth_quarter),
(sales_year, first_quarter, second_quarter, third_quarter, fourth_quarter),
(sales_year, first_quarter, second_quarter, third_quarter, fourth_quarter)
)
) D

2. Plamen Ratchev says:

This is interesting approach Mohammad. To my opinion if you are already using SQL Server 2005/2008 features it is much shorter syntax and clear to understand by using the UNPIVOT operator.

Hi Plamen,
I am back with a much clear version!

SELECT sales_year,
RIGHT(COALESCE(CAST(first_quarter AS VARCHAR)+ '1',
CAST(second_quarter AS VARCHAR) + '2',
CAST(third_quarter AS VARCHAR) + '3',
CAST(fourth_quarter AS VARCHAR) + '4'), 1) AS sales_quarter,
COALESCE(first_quarter, second_quarter, third_quarter, fourth_quarter) AS sales_amount
FROM QuarterlySales
GROUP BY GROUPING SETS
(
(sales_year, first_quarter),
(sales_year, second_quarter),
(sales_year, third_quarter),
(sales_year, fourth_quarter)
)
ORDER BY sales_year, sales_quarter;

The result sets
/
sales_year sales_quarter sales_amount
———– ————- ————-
2006 —— 1 ———– 211203.50
2006 —— 2 ———– 381594.95
2006 —— 3 ———– 439187.00
2006 —— 4 ———– 503155.80
2007 —— 1 ———– 231205.10
2007 —— 2 ———– 451101.25
2007 —— 3 ———– 601209.40
2007 —— 4 ———– 531907.30
/

Thank you!

Hi Plamen,
If you use 2005/2008 version it seems the best is to avoiding UNPIVOT table operator, and using this method:
SELECT sales_year,
sales_quarter,
sales_amount
FROM QuarterlySales
CROSS APPLY
(SELECT 1, first_quarter
UNION ALL
SELECT 2, second_quarter
UNION ALL
SELECT 3, third_quarter
UNION ALL
SELECT 4, fourth_quarter) D(sales_quarter, sales_amount);

Wouldn't running the query with many CAST operations over a large set affect its performance quite a bit? RE:
SELECT sales_year,
RIGHT(COALESCE(CAST(first_quarter AS VARCHAR)+ '1',
CAST(second_quarter AS VARCHAR) + '2',
CAST(third_quarter AS VARCHAR) + '3',
CAST(fourth_quarter AS VARCHAR) + '4'), 1) AS sales_quarter,
COALESCE(first_quarter, second_quarter, third_quarter, fourth_quarter) AS sales_amount
FROM QuarterlySales
GROUP BY GROUPING SETS
(
(sales_year, first_quarter),
(sales_year, second_quarter),
(sales_year, third_quarter),
(sales_year, fourth_quarter)
)
ORDER BY sales_year, sales_quarter;

7. Plamen Ratchev says:

Yes, the CAST function will have impact on performance on a very large set. Difficult to say how much without testing with real data.

8. Ben Brumm says:

Great article Plamen! I love the pivot feature as I find it’s easier to translate data this way in the database than to get some custom code to do it or do it in Excel.
I’ve used it a few times in SQL Server. Oracle has a similar keyword for doing this, which I’ve written about here: https://www.databasestar.com/oracle-sql-pivot/.
I also haven’t considered using the CROSS JOIN method before. I’ll have to keep that in mind.
Thanks!
Ben