Average Duration in Status - Gaps and Islands - sql

Question

I'm trying to calculate the average turnover time of a piece of equipment in REPAIR status.
I was able to create a query containing a list of equipments with their snapshotted status on each day.
+-----------------+--------------+--------+----------------------+------------+------------------+
| equipmentNumber | snapshotDate | status | previousSnapshotDate | prevStatus | statusChangeFlag |
+-----------------+--------------+--------+----------------------+------------+------------------+
| 123456 | 2018-04-29 | ONHIRE | 2018-04-28 | AVAILABLE | 1 |
| 123456 | 2018-04-30 | ONHIRE | 2018-04-29 | ONHIRE | 0 |
| 123456 | 2018-05-01 | ONHIRE | 2018-04-30 | ONHIRE | 0 |
| 123456 | 2018-05-02 | REPAIR | 2018-05-01 | ONHIRE | 1 |
| 123456 | 2018-05-03 | REPAIR | 2018-05-02 | REPAIR | 0 |
| 123456 | 2018-05-04 | ONHIRE | 2018-05-03 | REPAIR | 1 |
| 654321 | 2018-04-30 | REPAIR | 2018-04-29 | AVAILABLE | 1 |
| 654321 | 2018-05-01 | REPAIR | 2018-04-30 | REPAIR | 0 |
| 654321 | 2018-05-02 | REPAIR | 2018-05-01 | REPAIR | 0 |
+-----------------+--------------+--------+----------------------+------------+------------------+
So, in this example, we have 2 equipments, "123456" was in REPAIR status 2 days on 5/2 and 5/3, and "654321" was in REPAIR status 3 days on 4/30, 5/1, and 5/2. That would be an average repair turnaround time of (2+3) / 2 = 2.5 days.
I tried this algorithm (Detect consecutive dates ranges using SQL) but it doesn't seem to be quite working for my needs.

Answer 1

I attempt to answer Gaps and Islands using an Incrementing ID column, create one if one doesn't exist, and the ROW_NUMBER window function
CREATE TABLE T1
([equipmentNumber] int, [snapshotDate] datetime, [status] varchar(6), [previousSnapshotDate] datetime, [prevStatus] varchar(9), [statusChangeFlag] int)
;
INSERT INTO T1
([equipmentNumber], [snapshotDate], [status], [previousSnapshotDate], [prevStatus], [statusChangeFlag])
VALUES
(123456, '2018-04-29 00:00:00', 'ONHIRE', '2018-04-28 00:00:00', 'AVAILABLE', 1),
(123456, '2018-04-30 00:00:00', 'ONHIRE', '2018-04-29 00:00:00', 'ONHIRE', 0),
(123456, '2018-05-01 00:00:00', 'ONHIRE', '2018-04-30 00:00:00', 'ONHIRE', 0),
(123456, '2018-05-02 00:00:00', 'REPAIR', '2018-05-01 00:00:00', 'ONHIRE', 1),
(123456, '2018-05-03 00:00:00', 'REPAIR', '2018-05-02 00:00:00', 'REPAIR', 0),
(123456, '2018-05-04 00:00:00', 'ONHIRE', '2018-05-03 00:00:00', 'REPAIR', 1),
(654321, '2018-04-30 00:00:00', 'REPAIR', '2018-04-29 00:00:00', 'AVAILABLE', 1),
(654321, '2018-05-01 00:00:00', 'REPAIR', '2018-04-30 00:00:00', 'REPAIR', 0),
(654321, '2018-05-02 00:00:00', 'REPAIR', '2018-05-01 00:00:00', 'REPAIR', 0)
;
;WITH cteX
AS(
SELECT
Id = ROW_NUMBER()OVER(ORDER BY T.equipmentNumber, T.snapshotDate)
,T.equipmentNumber
,T.snapshotDate
,T.[status]
,T.previousSnapshotDate
,T.prevStatus
,T.statusChangeFlag
FROM dbo.T1 T
),cteIsland
AS(
SELECT
Island = X.Id - ROW_NUMBER()OVER(ORDER BY X.Id)
,*
FROM cteX X
WHERE X.[status] = 'REPAIR'
)
SELECT * FROM cteIsland
Note the Island Column
Island Id equipmentNumber status
3 4 123456 REPAIR
3 5 123456 REPAIR
4 7 654321 REPAIR
4 8 654321 REPAIR
4 9 654321 REPAIR
Using the Island Column you can get the answer you need with this TSQL
;WITH cteX
AS(
SELECT
Id = ROW_NUMBER()OVER(ORDER BY T.equipmentNumber, T.snapshotDate)
,T.equipmentNumber
,T.snapshotDate
,T.[status]
,T.previousSnapshotDate
,T.prevStatus
,T.statusChangeFlag
FROM dbo.T1 T
),cteIsland
AS(
SELECT
Island = X.Id - ROW_NUMBER()OVER(ORDER BY X.Id)
,*
FROM cteX X
WHERE X.[status] = 'REPAIR'
)
SELECT
AvgDuration =SUM(Totals.IslandCounts) / (COUNT(Totals.IslandCounts) * 1.0)
FROM
(
SELECT
IslandCounts = COUNT(I.Island)
,I.equipmentNumber
FROM cteIsland I
GROUP BY I.equipmentNumber
) Totals
Answer
AvgDuration
2.50000000000000
Here's the SQLFiddle

Answer 2

That method should work to identify the repair periods:
select equipmentNumber, min(snapshotDate), max(snapshotDate)
from (select t.*,
row_number() over (partition by equipmentNumber order by snapshotDate) as seqnum
from t
) t
where status = 'REPAIR'
group by equipmentNumber, dateadd(day, - seqnum, snapshotDate);
You can get the average using a subquery:
select avg(datediff(day, minsd, maxsd) * 1.0)
from (select equipmentNumber, min(snapshotDate) as minsd, max(snapshotDate) as maxsd
from (select t.*,
row_number() over (partition by equipmentNumber order by snapshotDate) as seqnum
from t
) t
where status = 'REPAIR'
group by equipmentNumber, dateadd(day, - seqnum, snapshotDate)
) e;