title: Northwind SQL total orders per customer
body: <p>I've added a column <code>TotalOrders</code> to the <code>Customers</code> table.</p>
  
  <pre><code>ALTER TABLE customers ADD TotalOrders INT NULL
  </code></pre>
  
  <p>I'm trying to find the total number of orders per customer and add that value to this column, however i can't figure out what do i need to sum exactly</p>
  
  <pre><code>INSERT INTO customers (TotalOrders) SELECT SUM(...)
  </code></pre>