title: Subquery using Exists 1 or Exists *
body: <p>I used to write my EXISTS checks like this:</p>
  
  <pre><code>IF EXISTS (SELECT * FROM TABLE WHERE Columns=@Filters)
  BEGIN
     UPDATE TABLE SET ColumnsX=ValuesX WHERE Where Columns=@Filters
  END
  </code></pre>
  
  <p>One of the DBA's in a previous life told me that when I do an <code>EXISTS</code> clause, use <code>SELECT 1</code> instead of <code>SELECT *</code></p>
  
  <pre><code>IF EXISTS (SELECT 1 FROM TABLE WHERE Columns=@Filters)
  BEGIN
     UPDATE TABLE SET ColumnsX=ValuesX WHERE Columns=@Filters
  END
  </code></pre>
  
  <p>Does this really make a difference?</p>