title: Exists / not exists: 'select 1' vs 'select field'
body: <p>Which one of the two would perform better(I was recently accused of not being careful with my code because I used the later in Oracle):</p>
  
  <pre><code>Select * 
  from Tab1
  Where (not) exists(Select 1 From Tab2 Where Tab1.id = Tab2.id)
  
  
  Select * 
  from Tab1
  Where (not) exists(Select Field1 From Tab2 Where Tab1.id = Tab2.id)
  </code></pre>
  
  <p>Or are they both same?</p>
  
  <p>Please answer both from SQL Server perspective as well as Oracle perspective.</p>
  
  <p>I have googled (mostly from sql-server side) and found that there is still a lot of debate over this although my present opinion/assumption is the optimiser in both the RDMBS are mature enough to understand that all that is required from the subquery is a Boolean value.</p>