How to update a table based on criteria from that same table - sql-server

Question

In the image above you'll note the first 6 rows that shows 2 records for each StudentID. I am needing to UPDATE, for each group of StudentID's, the EndDate column value of the 2nd record with a value of ONE DAY LESS THAN the StatusEffectiveDate of the first record for the same StudentID. I am working with SQL Server 2014.
So the first record should look like:
Here is my SQL code:
SELECT *
FROM #TEMP_99RecordsNeedingEndDateUpdated
ORDER BY StudentID asc, StatusEffectiveDate desc
Any help/direction would be appreciated.

Answer 1

Using what ZLK stated with a CTE to update the rows.
;WITH cte AS
(SELECT
*
, DATEADD(DAY, -1, LAG(statuseffectivedate) OVER (PARTITION BY StudentID ORDER BY statuseffectivedate DESC)) AS NewDate
FROM #TEMP_99RecordsNeedingEndDateUpdated)
UPDATE cte
SET cte.enddate = cte.NewDate
WHERE cte.NewDate IS NOT NULL

Answer 2

Late to the party, but here's one to try as well:
BEGIN TRANSACTION
UPDATE [YourTable] SET EndDate = DATEADD(DAY, -1, t.MaxDate)
FROM
(
SELECT StudentID, MAX(StatusEffectiveDate) as MaxDate
FROM [YourTable]
GROUP BY StudentID
) t
WHERE [YourTable].StudentID = t.StudentID AND [YourTable].StatusEffectiveDate <> t.MaxDate
-- COMMIT TRANSACTION
-- ROLLBACK TRANSACTION
As others have stated, this has very limited constraints on your data.
Essentially, I'm updating the EndDate to a new value, based on a sub query for the MAX() date from the same student ID. Finally, to avoid updating all student records, I ensure that the StatusEffectiveDate is not the later date.

Answer 3

This has very limited constraints, notably always needing two rows - one 'Free' and one 'Other' - but if that is the case, you should be able to do a UNION query.
SELECT StudentID, Location, Status, EconDisCode, StatusEffDate, EndDate
FROM #TEMP_99RecordsNeedingEndDateUpdated
WHERE Status = 'Free'
UNION
SELECT StudentID, Location, Status, EconDisCode, StatusEffDate, (SELECT StatusEffDate-1 FROM #TEMP_99RecordsNeedingEndDateUpdated t2 WHERE Status = 'Free' AND t1.StudentID = t2.StudentID) AS EndDate
FROM #TEMP_99RecordsNeedingEndDateUpdated t1
WHERE Status = 'Other'
I think a fiddle example with the data would be helpful.

Answer 4

with cte as
( select *
, row_number over (partition by studentID order by StatusEffectiveDate desc ) as rnD
, row_number over (partition by studentID order by StatusEffectiveDate asc ) as rnA
from table t
)
select cte.StudentID, cte.Location, cte.Status, cte.EconDisCode, cte.StatusEffectiveDate
, cte.EndDate
from cte
where rnD == 1
union
select cteA.StudentID, cteA.Location, cteA.Status, cteA.EconDisCode, cteA.StatusEffectiveDate
, dateadd(d, -1, cteD.StatusEffectiveDate)
from cte cteA
join cte cteD
on cteA.StudentID = cteD.StudentID
and cteA.rnD = 1
and cteD.rnA = 1
order by studentID, StatusEffectiveDate desc
update cteA
set cteA.EndDate = dateadd(d, -1, cteD.StatusEffectiveDate)
from cte cteA
join cte cteD
on cteA.StudentID = cteD.StudentID
and cteA.rnD = 1
and cteD.rnA = 1
order by studentID, StatusEffectiveDate desc
Include actual text (not image) so can cut and paste