Question

I have following table in my database.

I am trying to write a query which returns some rows from the above table.

The returning list:

1. Should not contain duplicates of Currency2_Id

2. If there are duplicates of Currency2_Id found, the latest record should be returned

   For an example in above table there are two records which has Currency2_Id = 7. The latest record from those two is the record which has Date = 2012-12-28.
   So my final result should be something like this.

This is the query I tried.

SELECT Id, Currency1_Id, Rate, Currency2_Id, Date 
FROM currency_ex_rate_txn
GROUP BY Currency2_Id
ORDER BY Date DESC

But the resultset I get contains the record with Currency2_Id = 7 and Date = 2012-12-25 instead of the record with Currency2_Id = 7 and Date = 2012-12-28.
Any help would be appreciated.

Answer 1

Try this:

SELECT 
  c1.Id, 
  c1.Currency1_Id, 
  c1.Rate, 
  c1.Currency2_Id, 
  c1.`Date`
FROM currency_ex_rate_txn c1
INNER JOIN
(
    SELECT Currency2_Id, MAX(`date`) LatestDate
    FROM currency_ex_rate_txn
    GROUP BY Currency2_Id
) c2  ON c1.Currency2_Id = c2.Currency2_Id
     AND c1.`date`       = c2.LatestDAte
ORDER BY c1.`Date` DESC;