title: Subtracting Two Columns In SQL After Join
body: <p>I have one table called Orders</p>
  
  <pre><code>PurchaseID VARCHAR
  purchaseDate DATETIME
  purchasePrice FLOAT
  </code></pre>
  
  <p>I want to find the difference between the purchase price on one day versus another day - The puyrchaseID will be the same.(This is just an example table of course)</p>
  
  <pre><code>SELECT a.purchasePrice AS purchasePriceDay1 ,  b.purchasePrice AS  purchasePriceDay1
  from Orders a , Orders b
  where a.PurchaseID = b.PurchaseID
  </code></pre>
  
  <p>Would that actually work</p>