title: SQL query for simple table
body: <p>I have a table:</p>
  
  <pre><code> ( EmployeeID (int), CourseID (int))
  </code></pre>
  
  <p>It is 1 to many relation. Employee can have many courseID. </p>
  
  <pre><code>EmployeeID         
     1                  
     1                  
     2                  
     2                  
     3                  
     3                  
     3       
  
  CourseID            
     1                  
     2                  
     2                  
     3                  
     1                  
     2                  
     3      
  </code></pre>
  
  <p>for example I would like to know number of employee who has courseID 1 and 2</p>
  
  <pre><code>Select  COUNT([employee ID])
  From EmployeeTable
  Where courseID = 1 and courseID = 2
  </code></pre>
  
  <p>Answer should be 2 because only EmployeeID 1 and EmployeeID 3 has CourseID 1 and 2. </p>