title: Rewrite SQL Query- I need to replace NOT IN with Join
body: <p>I have a query in my production environment which is taking long time to execute. I did not write this query but I must find a way to make it quicker since it is causing a big performance issue at the moment. I need to replace NOT IN with Left Join but not sure how to rewrite it. It looks like following at the moment</p>
  
  <pre><code>SELECT TOP 1 IT.ITEMID
  FROM   (SELECT CAST(ITEMID AS NUMERIC) + 1 ITEMID
          FROM   Items
          WHERE  ISNUMERIC(ITEMID) = 1
                 AND CAST(ITEMID AS NUMERIC) &gt;= 50000) IT
  WHERE  IT.ITEMID NOT IN (SELECT CAST(ITEMID AS NUMERIC) ITEMID
                           FROM   Items
                           WHERE  ISNUMERIC(ITEMID) = 1)
  ORDER  BY IT.ITEMID 
  </code></pre>
  
  <p>Kindly suggest how am I supposed to rewrite it using Left Join for better performance. Any help/guidance is greatly appreciated. </p>