Detect samples with dates differences within same data column - sql-server

Question

Table:
How can I scan each individual SampleRef and flag the one that have any of the delivery dates more than 6 months apart. So from the sample above only SampleRef A has dates that are 6 months apart example 01/04/2013 and 16/02/2014 using T-SQL.
Result:
Thank you!

Answer 1

Couple other options for you:
MIN and MAX per SampleRef and difference of those greater than 6 months.
Or use LAG() and get the previous delivery date for each record and then see which one had a previous delivery greater than six months.
DECLARE #TestData TABLE
(
[SampleRef] CHAR(1)
, [DeliveryDate] DATE
);
INSERT INTO #TestData (
[SampleRef]
, [DeliveryDate]
)
VALUES ( 'A', '4/1/2013' )
, ( 'A', '2/3/2013' )
, ( 'A', '2/16/2014' )
, ( 'A', '6/12/2015' )
, ( 'A', '6/26/2015' )
, ( 'A', '6/26/2015' )
, ( 'A', '2/10/2015' )
, ( 'B', '6/26/2015' )
, ( 'B', '6/27/2015' )
, ( 'B', '6/28/2015' )
, ( 'B', '6/29/2015' )
, ( 'B', '6/30/2015' )
, ( 'B', '7/1/2015' );
--This looks at all dates per sampleref, min and max and filters those greater than 6 months
SELECT *
FROM (
SELECT [SampleRef]
, MIN([DeliveryDate]) AS [MinDeliveryDate]
, MAX([DeliveryDate]) AS [MaxDeliveryDate]
FROM #TestData
GROUP BY [SampleRef]
) AS [SampleRef]
WHERE DATEDIFF(
MONTH
, [SampleRef].[MinDeliveryDate]
, [SampleRef].[MaxDeliveryDate]
) > 6;
--This will get the prior delivery date for each record and then you can see all where there was a span greater than six months.
SELECT *
, DATEDIFF(
MONTH
, [SampleRef].[PreviousDelivery]
, [SampleRef].[DeliveryDate]
) AS [MonthSincePreviousDelivery]
FROM (
SELECT *
, LAG([DeliveryDate], 1, [DeliveryDate]) OVER ( PARTITION BY [SampleRef]
ORDER BY [DeliveryDate]
) AS [PreviousDelivery]
FROM #TestData
) AS [SampleRef]
WHERE DATEDIFF(
MONTH
, [SampleRef].[PreviousDelivery]
, [SampleRef].[DeliveryDate]
) > 6;

Answer 2

--Is there a record belonging to a SampleRef, where for any row, there is an absence of any
--delivery within six months prior, however there is some prior delivery
SELECT
DISTINCT T1.SampleRef FROM YourTable T1
WHERE EXISTS(
SELECT 0 FROM YourTable T2
WHERE
T1.SampleRef = T2.SampleRef And
Not EXISTS( -- was there no delivery in last 6 months
SELECT 0 FROM YourTable T3
WHERE T3.SampleRef = T2.SampleRef
AND
T3.DeliverYdate >= DATEADD(mm,-6,T2.DeliveryDate)
AND
T3.DeliveryDate < T2.DeliveryDate
)
And Exists --check that there was howevwer a prior delivery
(
SELECT 0 FROM YourTable T4
WHERE T4.SampleRef = T2.SampleRef
AND
T4.DeliverYdate < T2.DeliveryDate
)
)

Answer 3

You can use ROW_NUMBER() to order the samples within a SampleRef, then join that ordered set to itself and find any records where the next available sample is more than 6 months later. (Note that the example code below won't tell you if it's been more than 6 months since the final sample in the set - you could modify the query to do so if necessary)
You didn't specify a name for the table, so replace YourTableNameHere in the query below with the name of your table.
WITH SamplesNumberedByGroup AS (
SELECT
SampleRef,
DeliveryDate,
ROW_NUMBER() OVER (PARTITION BY SampleRef ORDER BY DeliveryDate) AS 'SampleNum'
FROM
YourTableNameHere
)
SELECT
DISTINCT
S.SampleRef
FROM
SamplesNumberedByGroup S
INNER JOIN SamplesNumberedByGroup S2 ON S.SampleRef = S2.SampleRef AND S2.SampleNum = S.SampleNum + 1
WHERE
S2.DeliveryDate > DATEADD(MONTH,6,S.DeliveryDate);
If you want to see each sample where the next available sample is more than 6 months away (instead of just seeing which sampleref has a gap of at least 6 months), use the code below instead.
WITH SamplesNumberedByGroup AS (
SELECT
SampleRef,
DeliveryDate,
ROW_NUMBER() OVER (PARTITION BY SampleRef ORDER BY DeliveryDate) AS 'SampleNum'
FROM
YourTableNameHere
)
SELECT
S.SampleRef
,S.Price
,S.DeliveryDate
FROM
SamplesNumberedByGroup S
INNER JOIN SamplesNumberedByGroup S2 ON S.SampleRef = S2.SampleRef AND S2.SampleNum = S.SampleNum + 1
WHERE
S2.DeliveryDate > DATEADD(MONTH,6,S.DeliveryDate);
If you need to include any entries that are more than 6 months old but do not have a "next" entry as well, then replace INNER JOIN with LEFT OUTER JOIN and add OR (S2.DeliveryDate IS NULL AND GETDATE() > DATEADD(MONTH,6,S.DeliveryDate) to the where statement.

Answer 4

Use EXISTS() to check if there is any row where the next higher row for the same SampleRef is more than 6 months DATEDIFF.