Question

Having some problems while trying to optimize my SQL.

I got 2 tables like this:

Names
id, analyseid, name

Analyses
id, date, analyseid.

I want to get the newest analyse from Analyses (ordered by date) for every name (they are unique) in Names. I can’t really see how to do this without using 2 x nested selects.

My try (Dont get confused about the names. It’s the same principle):

SELECT
 B.id,
 B.chosendatetime,
 vStockNames.name
FROM
 vStockNames
INNER JOIN
 (
 SELECT TOP 1
  vAnalysesHistory.id,
  vAnalysesHistory.chosendatetime,
  vAnalysesHistory.companyid
 FROM
  vAnalysesHistory
 ORDER BY
  vAnalysesHistory.chosendatetime DESC
 ) AS B
ON
 B.companyid = vStockNames.stockid

In my example the problem is that i only get 1 row returned (because of top 1). But if I exclude this, I can get multiple analyses of the same name.

Can you help me ? – THanks in advance.

Answer 1

SQL Server 2000+:

 SELECT (SELECT TOP 1 
                a.id
           FROM vAnalysesHistory AS a 
          WHERE a.companyid = n.stockid 
       ORDER BY a.chosendatetime DESC) AS id,
        n.name, 
        (SELECT TOP 1 
                a.chosendatetime 
           FROM vAnalysesHistory AS a 
          WHERE a.companyid = n.stockid 
       ORDER BY a.chosendatetime DESC) AS chosendatetime
   FROM vStockNames AS n 

SQL Server 2005+, using CTE:

WITH cte AS (
   SELECT a.id,
          a.date,
          a.analyseid,
          ROW_NUMBER() OVER(PARTITION BY a.analyseid
                                ORDER BY a.date DESC) AS rk
     FROM ANALYSES a)
SELECT n.id, 
       n.name,
       c.date
  FROM NAMES n
  JOIN cte c ON c.analyseid = n.analyseid
            AND c.rk = 1

…without CTE:

SELECT n.id, 
       n.name,
       c.date
  FROM NAMES n
  JOIN (SELECT a.id,
               a.date, 
               a.analyseid,
               ROW_NUMBER() OVER(PARTITION BY a.analyseid
                                     ORDER BY a.date DESC) AS rk
          FROM ANALYSES a) c ON c.analyseid = n.analyseid
                            AND c.rk = 1