How to conditionally select records from SQL Server - sql

Question

Friends,
I have a SQL problem I could use help on. I'm working with SQL Server 2008.
The use case is the following. We have a system where users watch videos, and each time a user watches a video, we record that activity. We capture three properties each time; assetid (an asset is a video), customerid, and status.
A record can have three different statuses; 'completion', 'playing', and 'start'.
The person who wrote this part of the system is not a developer, and instead of of updating the status of an existing record, inserts a new duplicate record each time a user watches a video. Therefore we have thousands of duplicate records. Here is a sample dataset
The problem I need to solve is to select a record by assetid, customerid, and status. I need to choose a record that has a status of 'completion' if it exists.
If a record has a status of 'playing', but no record with the same assetid and customerid with a status of 'completion' exists, then choose that record.
If a record has a status of 'start', but no record with the same assetid and customerid with a status of either 'completion' or 'playing' exists, then choose that record.
Here is sample code where I tried to use a CASE statement to solve the problem. I also tried another case statement with a NOT IN subquery, but without success.
INSERT INTO #ViewTime (AssetID, CustomerID, ViewTime)
SELECT
tt.customerid, tt.assetId, tt.assetstatus,
CASE WHEN
tt.AssetStatus = 'COMPLETION'
AND
ISNUMERIC(timeposition) = 1
THEN
CONVERT(Numeric(18,3), timePosition)
WHEN
tt.AssetStatus = 'PLAYING'
AND
ISNUMERIC(timeposition) = 1
THEN
CONVERT(Numeric(18,3), timePosition)
WHEN
tt.AssetStatus = 'START'
AND
ISNUMERIC(timeposition) = 1
THEN
CONVERT(Numeric(18,3), timePosition)
ELSE null
END AS ViewTime
FROM
TableAssetTracking tt
inner join TableAssets ta
on tt.AssetID = ta.AssetID
WHERE
tt.timePosition is not null
AND
AssetBuffering is null
Any suggestions would be greatly appreciated. Thanks, Derek

Answer 1

The problem I need to solve is to select a record by assetid, customerid, and status.
I need to choose a record that has a status of 'completion' if it exists.
select distinct assetID, CustomerID
from table
where status = 'complete'
If a record has a status of 'playing', but no record with the same assetid and customerid with a status of 'completion' exists, then choose that record.
select assetID, CustomerID
from table
where status = 'playing'
except
select assetID, CustomerID
from table
where status = 'complete'
If a record has a status of 'start', but no record with the same assetid and customerid with a status of either 'completion' or 'playing' exists, then choose that record.
select assetID, CustomerID
from table
where status = 'start'
except
select assetID, CustomerID
from table
where status in ('complete', 'playing')
The above is not going to give you ViewTime that I see in the example
It was not in the requirements statement
select *
from
( select assetID, CustomerID, status, ViewTime
, row_number() over (partition by assetID, CustomerID order by status, ViewTime desc) as rn
from table
where status in ('complete', 'playing', 'start')
) tt
where tt.rn = 1

Answer 2

There are numerous ways to do this. Here is one.
I am going to use psuedocode because the tables in your sample code don't match the description in your question. You will have to adapt this technique to your tables.
SELECT DISTINCT t.AssetId, t.CustomerId, (
SELECT TOP 1 Status
FROM MyTable t1
WHERE t1.AssetId=t.AssetId
AND t1.CustomerId=t.CustomerId
ORDER BY CASE t1.Status
WHEN 'Completion' THEN 0
WHEN 'Playing' THEN 1
WHEN 'Started' THEN 2
ELSE 3
END ASC
) AS Status
FROM MyTable t

Answer 3

I did this in order to show you a broad way of looking at your data. You want to REALLY identify the last record that was inserted into your table for each person and video. So we get the last one, and then get the status for that record.
IF OBJECT_ID('tempdb..#lastRecord') IS NOT NULL DROP TABLE #lastRecord
SELECT
max(trackingassetdatecreated) dt,
assetid,
customerid,
INTO #lastRecord
FROM
TableAssetTracking
GROUP BY
assetid,
customerid
SELECT
t.assetstatus,
lr.*
FROM
TableAssetTracking t
INNER JOIN
#lastRecord lr on
lr.trackingassetdatecreated = t.trackingassetdatecreated
and lr.assetid = t.assetid
and lr.customerid = t.customerid