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SCD using date- Derive Effective From and Effective To Date using SQL

We can able to maintain old historical and current data (SCD) using the date column. Let me show you people how to write a small query to achieve it.

For example, Assume we have a column called currency which has currency values of all the countries and your business needs it to keep it uniform, say convert all currency of different countries to USD, so it will be easy for Business judgement and analysis.

For this, let me take an example of Yahoo! Finance. Yahoo! Finance API provides us currency conversion of all country based on time. I am not here going to tell how to pull the data from Yahoo! Finance API, But I am using such data which I pulled to explain how SCD can be achieved.

Below is a image, which depicts, the data which we got from Yahoo! Finance.


We wanted this to get converted as shown below:


Where we wanted to derive Effective_To column, which indicates, from one date to other date, the currency was so & so for a country against USD.

We can achieve this using Row_Number(). (Remember, we have built in Function in SQL Server from 2012 onwards to achieve the same)
Because, I am working on SQL Server 2008, this may help few people and below is query to do that.

SELECT From_Currency
      ,To_Currency
      ,Effective_From
      ,Exchange_Rate
      ,Row_Number() OVER (
            PARTITION BY From_Currency ORDER BY Effective_Date DESC
            )  AS RnkNxt
INTO #TEMP1
FROM Yahoo_Exchange_Rate

SELECT From_Currency
      ,To_Currency
      ,Effective_From
      ,Exchange_Rate
      ,Row_Number() OVER (
            PARTITION BY From_Currency ORDER BY Effective_Date DESC
            ) + 1 AS RnkNxt
INTO #TEMP2
FROM Yahoo_Exchange_Rate

SELECT Distinct O.From_Currency
      ,O.To_Currency
      ,Cast(Effective_Date As Datetime) As Effective_From
      ,Cast(Exchange_Rate As Decimal(15,8)) As Exchange_Rate
      ,(
            SELECT DateAdd(dd, - 1, Effective_Date)
            FROM #Temp1 T
            WHERE T.RnkNxt = O.Rnk
                  AND T.From_Currency = O.From_Currency
            ) AS Effective_To
FROM #TEMP2 O


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