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POSQL Server select distinct latest values
 

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    <p>I have a table that has a ton of rows (>10K). Most of the rows have duplicate <strong>role</strong> values associated with the <strong>username</strong>. </p> <p>What I am trying to do is select rows by distinct AND latest <strong>role</strong> added by <strong>request_id</strong>. I almost have it, but the part that is kicking my tail is there are <code>null</code> values in some of the <strong>request_id</strong> fields because those requests were made before that column was added. I <strong>STILL</strong> need to include them in the <code>select statement</code> in case a user has not entered another request since the update.</p> <p>Here a example of my table structure:</p> <pre><code> id | uname | role | request_id 0 | jsmith | User | null 1 | jsmith | Admin | null 2 | jsmith | Dude | null 3 | jsmith | Admin | 56 4 | jsmith | Dude | 56 5 | jsmith | Admin | 57 6 | jsmith | Dude | 57 </code></pre> <p><strong><em>This would be the desired result:</em></strong></p> <pre><code>0 | jsmith | User | null 5 | jsmith | Admin | 57 6 | jsmith | Dude | 57 </code></pre> <p>Here are the statements I've tried so far:</p> <h1>Join</h1> <pre><code>select distinct a.uname, a.role, a.request_id from ( select * from das_table ) b join das_table a on b.role = a.role and b.request_id = a.request_id where a.uname = 'jsmith' </code></pre> <p><strong>Result:</strong> This eliminates the rows with <strong>request_id</strong> = <code>NULL</code></p> <h1>MAX()</h1> <p>This didn't work for me I guess because <code>MAX()</code> doesn't count <code>null</code> values?</p> <pre><code>select distinct uname, role, max(request_id) as request_id from das_table where uname='jsmith' group by uname, role, request_id </code></pre> <h1>Similar questions I've looked at:</h1> <p>One caveat in my question that I think makes it different from the others I've researched is the <code>request_id</code> having the possibility of being null.</p> <p><a href="https://stackoverflow.com/questions/1918556/sql-select-distinct-values-from-1-column">Select distinct values from 1 column</a> | <a href="https://stackoverflow.com/questions/13461902/sql-server-select-distinct-by-one-column-and-by-another-column-value">SQL Server : select distinct by one column and by another column value</a> | <a href="https://stackoverflow.com/questions/2247401/sql-server-select-distinct-hell">SQL Server select distinct hell</a></p>
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