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