title: having trouble writing a query that list all salesmen that did not sell to a particular customer
body: <p>I was successful in writing the query that lists salesmen that did sell to a particular customer, but not those that have not. I suspect it is because the same salesmen that sold to the specific customer, also sold to other customers.   </p>
  
  <pre><code>  select a.name from salesperson a inner join orders b on 
    a.salesperson_id = b.salesperson_id where cust_id="4";
  </code></pre>
  
  <p>I was thinking that modifying the same query like this would do the trick:</p>
  
  <pre><code>  .... a.salesperson_id &lt;&gt; b.salesperson_id where cust_id="4";
  </code></pre>
  
  <p>But the result lists all the salesmen. This is most likely due to the  fact that the same salesmen that were returned in the original query, also sold to other customers</p>
  
  <p>The 3 tables look like this: </p>
  
  <pre><code>               Salesperson table
  
                       salesperson_ID,     Name,     Age,      Salary
  
                           1                   Abe        61       140000
                           2                   Bob        34        44000
                           5                  Chris       34        40000
                           7                   Dan        41        52000
                           8                   Ken        57       115000
                           11                  Joe        38        38000
  
  
                     Customer table
  
                     cust_ID,       Name,     City           Industry Type
  
                        4            faralon    sacramento            H
                        6             Apple       cupertino           S
                        7            Honda       NY                   B
                        9            Kolb      Oshkosh                B
  
  
  
  
            Orders table
  
               Number,        Order_date,   cust_id,  salesperson_id,   Amount
  
              10              8/2/1996           4             2         540
               20             1/30/1999          4             8        1800
               30             7/14/1995          9             1         460
              40             1/29/1998           7             2        2400
              50             2/3/1998            6              7        600
              60             3/2/1998            6              7        720
              70             5/6/1998            9              7        150
  </code></pre>
  
  <p>Any help would be greatly appreciated. ~Alpinehyker</p>