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POCalculate the previous value in T-SQL (update)
 

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  1. POCalculate the previous value in T-SQL (update)
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    <p>I am struggling a little, not to say, much with some SQL logic.</p> <p><em>Example of the Data set</em></p> <pre><code>wid CCVnr Amount Reference Seq Month ColumIwant=PreviousAmount 11 15946 20 50 1 1/1/2013 NULL 12 15946 20 50 2 1/2/2013 NULL 13 15946 20 50 3 1/3/2013 NULL 14 15946 20 50 4 1/4/2013 NULL 15 15946 20 50 5 1/5/2013 NULL 16 15946 20 50 6 1/6/2013 NULL 35 15946 20 50 1 1/1/2013 NULL 36 15946 10 50 2 1/2/2013 20 37 15946 10 50 3 1/3/2013 20 38 15946 10 50 4 1/4/2013 20 39 15946 10 50 5 1/5/2013 20 40 15946 10 50 6 1/6/2013 20 88 15946 10 50 1 1/1/2013 20 89 15946 20 50 2 1/2/2013 NULL 90 15946 25 50 3 1/3/2013 10 91 15946 25 50 4 1/4/2013 10 92 15946 25 50 5 1/5/2013 10 93 15946 25 50 6 1/6/2013 10 </code></pre> <p>The 5 first columns I have, I want to 'calculate' the last column: PreviousAmount. The problem for me is that every time all 6 months are (re)loaded so it's not enough to look at the 'changed' value, you also have to take into account the history is there to. <br> (I first had a piece of code with a CTE comparing one row to the next but like this I'm missing the history...) </p> <p>Situation here is: a client has an amount he wants to pay per month he can change: In this case the changes it from 20 to 10 to 25.</p> <p>I've uploaded a CSV-file or the very dataset I'm working with here: <a href="https://mega.co.nz/#!oZhC0RxB!CzzMx3Yr6Kx1_1N9scuNqwJnqoZDGUXte47iOPkLG-E" rel="nofollow">https://mega.co.nz/#!oZhC0RxB!CzzMx3Yr6Kx1_1N9scuNqwJnqoZDGUXte47iOPkLG-E</a></p> <p>We using SQL Server 2008 R2. There are 20M rows like this in the table. So maybe a cursor is not the best option(?)</p> <p>Thanks a lot in advance for any help !! L</p> <p><br>UPDATE: I added a wid column because the original data set also holds a wid column. @<strong>Mark Bannister</strong> The logic is to look at 'Amount' and when for a certain month the Amount is changed by the user: * All the next months get updated when the 'New Amount' * We calculate the Previous Amount which is = the Amount is was before</p> <p>@<strong>Love2Learn</strong> also thanks for your comment. There are lots more columns but you have to know it's not easy to add more columns in the stackoverflow code block. Therefore I also uploaded a CSV file from which you can find the link. A relevant column I do have added is the 'wid'.</p> <p>Normally there should be enough info and columns to calculate this previous row. Thanks in advance! </p>
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    1. USlaurens
    1. USlaurens
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    1. COWhat is the logic for determining which row holds the "previous" value? What is the primary key on the table?
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      1. USJosef K
    2. COIs the entirety of your table schema just those five columns???
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      1. USEric J. Price
    3. COPlease include more information. There is no deterministic way to find the "previous row" with the data you've included in the question.
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      1. POCalculate the previous value in T-SQL (update)
      1. USAaron Bertrand
 

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