title: Oracle/SQL - Join one table multiple times to the same table
body: <p>I'm trying to wrap my brain around a query and hoping you can help.  I have two tables: a customer_table and a product_table that look like this</p>
  
  <pre><code>name    sku_num1    sku_num2    sku_num3    sku_num4
  ----------------------------------------------------    
  Bob     A           B           C           D
  Frank   E           A
  Tom     G
  Shelly  G           E
  Justin  E           G           A
  
  sku_num     widget_name
  -------------------
  A           widget_a
  B           widget_b
  C           widget_c
  D           widget_d
  </code></pre>
  
  <p>So what I want to do is return a list of all the customers who have at least 1 product whose SKU appears in the product table.  So with the above information I would receive back the records for</p>
  
  <p>Bob</p>
  
  <p>Frank</p>
  
  <p>Justin</p>
  
  <p>Any ideas how to do this?</p>