Question

I’ve got a table with an auto-increment number field As “No”, a date/time stamp As “Entry_Date”, and X, Y, Z fields. Every few minutes, My program inserts a new row with the current date/time.

I need a query that will give the first row entered for each day for the past 365 days (or whatever value I want to use). Please help…

Answer 1

I’d use ROW_NUMBER and partition by date. Nice and simple: (Note this is 2008, for use of DATE)

CREATE TABLE #TestDatePartition
(
    ID int IDENTITY(1,1),
    EntryTime datetime
)

INSERT INTO #TestDatePartition(EntryTime)
SELECT GETDATE() UNION ALL
SELECT DATEADD(HH, 1, GETDATE()) UNION ALL
SELECT DATEADD(HH, 2, GETDATE()) UNION ALL
SELECT DATEADD(DAY, 1, GETDATE()) UNION ALL
SELECT DATEADD(HH, 26, GETDATE()) UNION ALL
SELECT DATEADD(DAY, 6, GETDATE())

SELECT ID, EntryTime FROM (
SELECT ID, EntryTime, ROW_NUMBER() OVER (PARTITION BY CAST(EntryTime AS DATE) ORDER BY EntryTime ASC) AS RowNumber FROM #TestDatePartition
) SubTable
WHERE SubTable.RowNumber = 1