Improve performance on CTE with sub-queries - tsql

Question

I have a table with this structure:
WorkerID Value GroupID Sequence Validity
1 '20%' 1 1 2018-01-01
1 '10%' 1 1 2017-06-01
1 'Yes' 1 2 2017-06-01
1 '2018-01-01' 2 1 2017-06-01
1 '17.2' 2 2 2017-06-01
2 '10%' 1 1 2017-06-01
2 'No' 1 2 2017-06-01
2 '2016-03-01' 2 1 2017-06-01
2 '15.9' 2 2 2017-06-01
This structure was created so that the client can create customized data for a worker. For example Group 1 can be something like "Salary" and Sequence is one value that belongs to that Group like "Overtime Compensation". The column Value is a VARCHAR(150) field and the correct validation and conversation is done in another part of the application.
The Validity column exist mainly for historical reasons.
Now I would like to show, for the different workers, the information in a grid where each row should be one worker (displaying the one with the most recent Validity):
Worker 1_1 1_2 2_1 2_2
1 20% Yes 2018-01-01 17.2
2 10% No 2016-03-01 15.9
To accomplish this I created a CTE that looks like this:
WITH CTE_worker_grid
AS
(
SELECT
worker,
/* 1 */
(
SELECT top 1 w.Value
FROM worker_values AS w
WHERE w.GroupID = 1
AND w.Sequence = 1
ORDER BY w.Validity DESC
) AS 1_1,
(
SELECT top 1 w.Value
FROM worker_values AS w
WHERE w.GroupID = 1
AND w.Sequence = 2
ORDER BY w.Validity DESC
) AS 1_2,
/* 2 */
(
SELECT top 1 w.Value
FROM worker_values AS w
WHERE w.GroupID = 2
AND w.Sequence = 1
ORDER BY w.Validity DESC
) AS 2_1,
(
SELECT top 1 w.Value
FROM worker_values AS w
WHERE w.GroupID = 2
AND w.Sequence = 2
ORDER BY w.Validity DESC
) AS 2_2
)
GO
This produces the correct result but it's very slow as it creates this grid for over 18'000 worker with almost 30 Groups and up to 20 Sequences in each Group.
How could one speed up the process of a CTE of this magnitude? Should CTE even be used? Can the sub-queries be changed or re-factored out to speed up the execution?

Answer 1

Use a PIVOT!
+----------+---------+---------+------------+---------+
| WorkerId | 001_001 | 001_002 | 002_001 | 002_002 |
+----------+---------+---------+------------+---------+
| 1 | 20% | Yes | 2018-01-01 | 17.2 |
| 2 | 10% | No | 2016-03-01 | 15.9 |
+----------+---------+---------+------------+---------+
SQL Fiddle: http://sqlfiddle.com/#!18/6e768/1
CREATE TABLE WorkerAttributes
(
WorkerID INT NOT NULL
, [Value] VARCHAR(50) NOT NULL
, GroupID INT NOT NULL
, [Sequence] INT NOT NULL
, Validity DATE NOT NULL
)
INSERT INTO WorkerAttributes
(WorkerID, Value, GroupID, Sequence, Validity)
VALUES
(1, '20%', 1, 1, '2018-01-01')
, (1, '10%', 1, 1, '2017-06-01')
, (1, 'Yes', 1, 2, '2017-06-01')
, (1, '2018-01-01', 2, 1, '2017-06-01')
, (1, '17.2', 2, 2, '2017-06-01')
, (2, '10%', 1, 1, '2017-06-01')
, (2, 'No', 1, 2, '2017-06-01')
, (2, '2016-03-01', 2, 1, '2017-06-01')
, (2, '15.9', 2, 2, '2017-06-01')
;WITH CTE_WA_RANK
AS
(
SELECT
ROW_NUMBER() OVER (PARTITION BY WorkerID, GroupID, [Sequence] ORDER BY Validity DESC) AS VersionNumber
, WA.WorkerID
, WA.GroupID
, WA.[Sequence]
, WA.[Value]
FROM
WorkerAttributes AS WA
),
CTE_WA
AS
(
SELECT
WA_RANK.WorkerID
, RIGHT('000' + CAST(WA_RANK.GroupID AS VARCHAR(3)), 3)
+ '_'
+ RIGHT('000' + CAST(WA_RANK.[Sequence] AS VARCHAR(3)), 3) AS SMART_KEY
, WA_RANK.[Value]
FROM
CTE_WA_RANK AS WA_RANK
WHERE
WA_RANK.VersionNumber = 1
)
SELECT
WorkerId
, [001_001] AS [001_001]
, [001_002] AS [001_002]
, [002_001] AS [002_001]
, [002_002] AS [002_002]
FROM
(
SELECT
CTE_WA.WorkerId
, CTE_WA.SMART_KEY
, CTE_WA.[Value]
FROM
CTE_WA
) AS WA
PIVOT
(
MAX([Value])
FOR
SMART_KEY IN
(
[001_001]
, [001_002]
, [002_001]
, [002_002]
)
) AS PVT