convert rows to columns order by another column in sql server - sql

Question

I'm trying to convert this table
ID TestID Elapsed ActionID
===================================
1 1 16 a1
2 1 17 a2
3 1 13 a3
4 1 14 a4
5 2 19 a1
6 2 21 a2
7 2 11 a3
8 2 22 a4
To this
TestID a1 a2 a3 a4
======================================
1 16 17 13 14
2 19 21 11 22
is this possible?

Answer 1

Yes, if there is only one action id for each testid
There is the pivot operator that Ajoe mentioned, but I think the traditional
syntax is easier to understand (if not immediately obvious).
You group rows by testid, so you will get one row of results
per each testid. What you select is the "max" in each group where the acitionid is a certain one. Or the min, or the average, or the sum - this is
predicated on there being only one item in each group.
SELECT testid,
MAX(CASE WHEN actionid = 'a1' THEN elapsed ELSE null END) AS a1,
MAX(CASE WHEN actionid = 'a2' THEN elapsed ELSE null END) AS a2,
MAX(CASE WHEN actionid = 'a3' THEN elapsed ELSE null END) AS a3,
MAX(CASE WHEN actionid = 'a4' THEN elapsed ELSE null END) AS a4
FROM results
GROUP BY testid

Answer 2

If you are using SQL Server 2005 (or above), here's the query, with proof of concept. Enjoy:
--Proof of concept structure and data creation
create table #t (ID int, TestID int, Elapsed int, ActionID varchar(10))
insert into #t (ID, TestID, Elapsed, ActionID) values
(1, 1, 16, 'a1'),
(2, 1, 17, 'a2'),
(3, 1, 13, 'a3'),
(4, 1, 14, 'a4'),
(5, 2, 19, 'a1'),
(6, 2, 21, 'a2'),
(7, 2, 11, 'a3'),
(8, 2, 22, 'a4');
--end of structure and data creating
--actual query starts here
DECLARE #cols VARCHAR(1000)
DECLARE #sqlquery VARCHAR(2000)
SELECT #cols = STUFF(( SELECT distinct ',' + QuoteName([ActionID])
FROM #t FOR XML PATH('') ), 1, 1, '')
SET #sqlquery = 'SELECT * FROM
(SELECT TestID, Elapsed, ActionID
FROM #t ) base
PIVOT (SUM(Elapsed) FOR [ActionID]
IN (' + #cols + ')) AS finalpivot'
--Depending on your approach, you might want to use MAX instead of SUM.
--That will depend on your business rules
EXECUTE ( #sqlquery )
--query ends here
--proof of concept cleanup
drop table #t;
This will work no matter how many different values you have in ActionID. It dynamically assembles a query with PIVOT. The only way you can do PIVOT with dynamic columns is by assembling the the query dynamically, which can be done in SQL Server.
Other examples:
SQL Server PIVOT perhaps?
Pivot data in T-SQL
How do I build a summary by joining to a single table with SQL Server?