Select 1 Distinct Record per month by latest date - sql

Question

I have a list of data that looks like this:
Name Date Weight
Person 1 01/01/2014 89KG
Person 2 01/01/2014 62KG
Person 1 07/01/2014 88KG
Person 2 07/01/2014 62KG
Person 1 21/01/2014 85KG
Person 2 21/01/2014 63KG
What I would like to do is select only the records with a distinct name and are the latest dates in a given month. So for this example I would like to only select the person 1 and person 2 records for 21/01/2014 (as this is the latest date). I'm using SQL 2008.

Answer 1

Please see if this works for you.
Sample Data:
IF OBJECT_ID(N'tempdb..#TEMP') > 0
BEGIN
DROP TABLE #TEMP
END
CREATE TABLE #TEMP(Name VARCHAR(20),
WDate VARCHAR(20),
Weight VARCHAR(20))
INSERT INTO #TEMP
VALUES
('Person 1', '01/01/2014', '89KG'),
('Person 2', '01/01/2014', '62KG'),
('Person 1', '07/01/2014', '88KG'),
('Person 1', '07/01/2014', '88KG'),
('Person 2', '07/02/2014', '62KG'),
('Person 1', '21/01/2014', '85KG'),
('Person 2', '21/01/2014', '63KG');
Script:
;WITH cte_DateFormat
AS (
SELECT Name,
CONVERT(DATE, WDate, 103) AS WDate,
Weight
FROM #TEMP
)
, cte_Rank
AS (
SELECT ROW_NUMBER() OVER (PARTITION BY Name,
CAST(YEAR(WDate) AS VARCHAR(4)) + CAST(MONTH(WDate) AS VARCHAR(2)) ORDER BY WDate DESC) AS ID,
Name,
WDate,
Weight
FROM cte_DateFormat
)
SELECT Name,
WDate,
Weight
FROM cte_Rank
WHERE ID = 1
Cleanup Script:
IF OBJECT_ID(N'tempdb..#TEMP') > 0
BEGIN
DROP TABLE #TEMP
END

Answer 2

Please try using DENSE_RANK:
select
*
From (
select
*,
DENSE_RANK() over(PARTITION BY YEAR([Date]),
MONTH([Date])
ORDER BY [Date] desc) Rnk
From tbl
)x where Rnk=1

Answer 3

This will also work, using row partitioning:
SELECT Name, Date, Weight
FROM ( SELECT
Name,
Date,
Weight,
ROW_NUMBER() OVER ( PARTITION BY Name, MONTH(Date)
ORDER BY Date DESC) AS [RowNum]
FROM [YourTableHere]
) Tbl
WHERE Tbl.RowNum = 1
ORDER BY MONTH(Date), Name
Test Script:
DECLARE #Table TABLE (Name VARCHAR(20), Date Date, Weight VARCHAR(20))
INSERT INTO #Table (Name, Date, Weight)
VALUES ('Person 1', '1/1/2014', '89KG'),
('Person 2', '1/1/2014', '62KG'),
('Person 1', '1/7/2014', '88KG'),
('Person 2', '1/7/2014', '62KG'),
('Person 1', '1/21/2014', '85KG'),
('Person 2', '1/21/2014', '63KG'),
('Person 1', '2/1/2014', '84KG'),
('Person 2', '2/1/2014', '61KG'),
('Person 1', '2/11/2014', '83KG'),
('Person 2', '2/11/2014', '60KG')
SELECT Name, Date, Weight
FROM ( SELECT
Name,
Date,
Weight,
ROW_NUMBER() OVER ( PARTITION BY Name, MONTH(Date)
ORDER BY Date DESC) AS [RowNum]
FROM #Table
) Tbl
WHERE Tbl.RowNum = 1
ORDER BY MONTH(Date), Name