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PODetermine which columns have changed in rows of a table
 

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  1. PODetermine which columns have changed in rows of a table
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    <p>I have a SQL Server table which contains incremental <code>Measurement</code>s of several different <code>Attribute</code>s pertaining to various <code>Object</code>s:</p> <pre><code>MeasurementID ObjectID Attribute1 Attribute2 Attribute3 100 1 'blue' 111 'large' 101 1 'blue' 114 'large' 102 1 'red' 114 'large' 103 1 'red' 117 'large' 104 1 'cyan' 118 'large' 105 2 'blue' 450 'huge' 106 3 'blue' 450 'huge' 107 3 'red' 450 'huge' </code></pre> <p>My objective is to find an efficient query which, given a specific <code>ObjectID</code> tells me which attributes changed and when. For example, let's say <code>ObjectID=1</code>. <code>Attribute1</code> changed at <code>MeasurementID=102</code> (from <code>'blue'</code> to <code>'red'</code>), and similarly for <code>Attribute2</code> at <code>MeasurementID=101</code> and <code>MeasurementID=103</code>, and for <code>Attribute3</code> at no time (<code>NULL</code>). Conceptually, I'm looking for something which fulfills this pseudo-code definition:</p> <pre><code>CREATE FUNCTION GetMeasurementChanges (ObjectID int, AttributeName varchar) RETURNS @returnMeasurementIDs TABLE (MeasurementID int) -- rows of MeasurementIDs </code></pre> <p>I can think of a slow way to do it with poor performance by selecting into a temp table on an <code>Object</code>-by-<code>Object</code> basis and then iterating through the rows, testing each <code>Attribute</code>, but I suspect that's going to perform very poorly.</p> <p>Anyone got a trick or an analogous question they can point me to?</p> <p>Thanks!</p>
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    1. USjbeldock
    1. USjbeldock
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    1. COWhat version of SQL Server? Later version have useful analytical functions and earlier versions do not.
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      1. USNick.McDermaid
    2. COPlease see [this post regarding never declaring `varchar` without length](http://sqlblog.com/blogs/aaron_bertrand/archive/2009/10/09/bad-habits-to-kick-declaring-varchar-without-lengthhttp://sqlblog.com/blogs/aaron_bertrand/archive/2009/10/11/bad-habits-to-kick-avoiding-the-schema-prefix.aspx.aspx) and [this post regarding always using the schema prefix when creating and referencing objects](http://sqlblog.com/blogs/aaron_bertrand/archive/2009/10/11/bad-habits-to-kick-avoiding-the-schema-prefix.aspx).
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      1. USAaron Bertrand
 

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