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POSET NOCOUNT ON usage
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copied!<p>Inspired by <a href="https://stackoverflow.com/questions/1483383/is-this-stored-procedure-thread-safe-or-whatever-the-equiv-is-on-sql-server">this question</a> where there are differing views on SET NOCOUNT...</p> <blockquote> <p>Should we use SET NOCOUNT ON for SQL Server? If not, why not?</p> </blockquote> <p><strong>What it does</strong> Edit 6, on 22 Jul 2011</p> <p>It suppresses the "xx rows affected" message after any DML. This is a resultset and when sent, the client must process it. It's tiny, but measurable (see answers below)</p> <p>For triggers etc, the client will receive multiple "xx rows affected" and this causes all manner of errors for some ORMs, MS Access, JPA etc (see edits below)</p> <p><strong>Background:</strong></p> <p>General accepted best practice (I thought until this question) is to use <code>SET NOCOUNT ON</code> in triggers and stored procedures in SQL Server. We use it everywhere and a quick google shows plenty of SQL Server MVPs agreeing too.</p> <p>MSDN says this can break a <a href="http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldataadapter.aspx" rel="noreferrer">.net SQLDataAdapter</a>.</p> <p>Now, this means to me that the SQLDataAdapter is limited to utterly simply CRUD processing because it expects the "n rows affected" message to match. So, I can't use:</p> <ul> <li>IF EXISTS to avoid duplicates (no rows affected message) <em>Note: use with caution</em></li> <li>WHERE NOT EXISTS (less rows then expected</li> <li>Filter out trivial updates (eg no data actually changes)</li> <li>Do any table access before (such as logging)</li> <li>Hide complexity or denormlisation</li> <li>etc</li> </ul> <p>In the question marc_s (who knows his SQL stuff) says do not use it. This differs to what I think (and I regard myself as somewhat competent at SQL too).</p> <p>It's possible I'm missing something (feel free to point out the obvious), but what do you folks out there think?</p> <p>Note: it's been years since I saw this error because I don't use SQLDataAdapter nowadays.</p> <p><strong>Edits after comments and questions:</strong></p> <p>Edit: More thoughts...</p> <p>We have multiple clients: one may use a C# SQLDataAdaptor, another may use nHibernate from Java. These can be affected in different ways with <code>SET NOCOUNT ON</code>.</p> <p>If you regard stored procs as methods, then it's bad form (anti-pattern) to assume some internal processing works a certain way for your own purposes.</p> <p>Edit 2: a <a href="https://stackoverflow.com/questions/1354362">trigger breaking nHibernate question</a>, where <code>SET NOCOUNT ON</code> can not be set</p> <p>(and no, it's not a duplicate of <a href="https://stackoverflow.com/questions/995589/set-nocount-off-or-return-rowcount">this</a>)</p> <p>Edit 3: Yet more info, thanks to my MVP colleague</p> <ul> <li><a href="http://support.microsoft.com/?scid=kb%3Ben-us%3B240882&x=4&y=9" rel="noreferrer">KB 240882</a>, issue causing disconnects on SQL 2000 and earlier</li> <li><a href="http://sqlmag.com/sql-server-2000/seeing-believing" rel="noreferrer">Demo of performance gain</a> </li> </ul> <p>Edit 4: 13 May 2011</p> <p><a href="https://stackoverflow.com/q/5880413/27535">Breaks Linq 2 SQL too when not specified?</a></p> <p>Edit 5: 14 Jun 2011</p> <p>Breaks JPA, stored proc with table variables: <a href="https://stackoverflow.com/q/6344631/27535">Does JPA 2.0 support SQL Server table variables?</a></p> <p>Edit 6: 15 Aug 2011</p> <p>The SSMS "Edit rows" data grid requires SET NOCOUNT ON: <a href="https://stackoverflow.com/q/7067329/27535">Update trigger with GROUP BY</a></p> <p>Edit 7: 07 Mar 2013</p> <p>More in depth details from @RemusRusanu:<br> <a href="https://stackoverflow.com/questions/1915405/does-set-nocount-on-really-make-that-much-of-a-performance-difference/1918085#1918085">Does SET NOCOUNT ON really make that much of a performance difference</a></p>

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