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POSelect based on matching columns
 

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    <p>I have two tables both containing various companies. I want to select everything from <code>tableOne</code> that appears in <code>tableTwo</code> (in fact, only if it appears in <code>tableTwo</code>). I’ll do this by comparing their <code>companyID</code> fields. They must also have the same value for a column <code>someYear</code>. So in other words, I want to return the companies that appear in <code>tableTwo</code> from <code>tableOne</code>, if and only if their <code>someYear</code> columns match.</p> <pre><code>tableOne companyID someYear --------- -------- 1 2010 2 2009 3 2011 1 2011 7 2009 tableTwo companyID someYear --------- -------- 1 2010 2 2008 3 2011 4 2011 5 2009 </code></pre> <p>I want to return <code>1</code> and <code>3</code> (company <code>2</code>’s year differs so I don’t want it). My useless attempt:</p> <pre><code>SELECT one.* FROM tableOne one, tableTwo two WHERE one.[companyID] in ( SELECT DISTINCT companyID FROM tableTwo ) and one.someYear = two.someYear; </code></pre> <p>The problem here is that it returns millions of rows, when both tables contain less than 10,000 entries. I can't recreate the output exactly because of sensitive information. The table/column names here are all made up as I'm sure you can tell. Also I should probably point out that <strong>neither table appears to have a primary key</strong>. I assume that causes them to have nothing to match on. I’m using SQL Server 2008. Any help would be hugely appreciated. </p>
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