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    <p>My first instinct would be to pump your 5000 inputs into a single-column temporary table X, possibly index it, and then use:</p> <pre><code>SELECT X.thecol FROM X JOIN ExistingTable USING (thecol) </code></pre> <p>to get the ones that are present, and (if both sets are needed)</p> <pre><code>SELECT X.thecol FROM X LEFT JOIN ExistingTable USING (thecol) WHERE ExistingTable.thecol IS NULL </code></pre> <p>to get the ones that are absent. Worth benchmarking, at least.</p> <p>Edit: as requested, here are some good docs &amp; tutorials on temp tables in SQL Server. <a href="http://www.sqlteam.com/article/temporary-tables" rel="nofollow noreferrer">Bill Graziano</a> has a simple intro covering temp tables, table variables, and global temp tables. <a href="http://www.sql-server-performance.com/articles/per/temp_tables_necessary_p1.aspx" rel="nofollow noreferrer">Randy Dyess</a> and <a href="http://sqlserver-qa.net/blogs/perftune/archive/2008/01/17/3228.aspx" rel="nofollow noreferrer">SQL Master</a> discuss performance issue for and against them (but remember that if you're getting performance problems you do want to benchmark alternatives, <em>not</em> just go on theoretical considerations!-).</p> <p>MSDN has articles on <a href="http://msdn.microsoft.com/en-us/library/ms190768.aspx" rel="nofollow noreferrer">tempdb</a> (where temp tables are kept) and <a href="http://msdn.microsoft.com/en-us/library/ms175527.aspx" rel="nofollow noreferrer">optimizing</a> its performance.</p>
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    1. CO"single-column temporary table X" -- appreciate if you could clarify this. I think this point is important. temporary table you mean creating a physical table or?
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    2. COCREATE TABLE #X (thecol VARCHAR(30)) makes the temporary table (the leading # in the name is what makes it temporary) -- it lasts only as long as the procedure or session that creates it.
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    3. COIn my scenario, (1) why a temporary table is better? Compared with creating another physical table? (2) for the temporary table, what is your advice about when we create it/when we drop it. i.e. create a new temporary table each time when there is 5000 batch queries and drop after join, or create temp table only once?
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