title: "Where not exists" vs "left outer join" in oracle sql
body: <p>I have a simple SQL query:</p>
  
  <pre><code>SELECT  
         columnA, columnB, columnC...  
   FROM  
         (SELECT    
               columnA, columnB, columnC...  
          FROM   
                SomeTable) Table1  
    WHERE NOT EXISTS  
          (SELECT   
                 columnA  
            FROM  
                 SomeOtherTable st  
            WHERE  
                 st.columnB = Table1.columnB)
  </code></pre>
  
  <p>Can anyone give me a suggestion how to rewrite this query for better performance? I mean to include the <code>WHERE NOT EXISTS</code> clause in Table1.</p>