title: How to count how many times that each pair of item has same order id in mySQL
body: <p>i want to count that how many times that each pair of SKU have been ordered together(have same orderid)<br>
  I have an <strong>order</strong> table of customers that has 2 column <strong>ORDERID</strong> and <strong>SKUID</strong><br>
  for an example  </p>
  
  <pre><code>ORDERID SKUID  
  1       1  
  1       2  
  1       3  
  2       1  
  2       2  
  2       4  
  3       1  
  3       4
  </code></pre>
  
  <p>i want a result table as</p>
  
  <pre><code>SKU1 SKU2  COUNT  
  1    2     2  
  1    3     1  
  1    4     2  
  2    3     1  
  2    4     1  
  3    4     0
  </code></pre>
  
  <p>thank you</p>