title: Reduce Duplicate results in SQL query
body: <pre><code>    select
  rtrim(p.firstname) + ' ' + p.lastname as [instructor name], 
  lesson_type.lessonname, 
  location.locationname, 
  lesson_1.lessondate
  from person as p inner join lesson as l 
  on p.personid = l.employeeid 
  inner join location 
  on l.locationid = location.locationid 
  inner join lesson as lesson_1 
  on p.personid = lesson_1.employeeid and location.locationid = lesson_1.locationid 
  inner join lesson_type 
  on l.lessontypeid = lesson_type.lessontypeid and lesson_1.lessontypeid = lesson_type.lessontypeid
  order by [instructor name] ASC
  </code></pre>
  
  <p>How can I not have duplicate Lesson Dates for the same Location Name and Lesson Name?  Here is my output:</p>
  
  <pre><code>instructor name                 lessonname      locationname    lessondate
  ------------------------------- --------------- --------------- ----------
  Anna Dillinger                  Diamond         Brighton Ski    2014-01-12
  Anna Dillinger                  Newbie          Steamboat       2014-01-01
  Anna Dillinger                  Intermediate    Steamboat       2014-01-01
  Anna Dillinger                  Newbie          Mt. Holly       2014-02-12
  Anna Dillinger                  Newbie          Mt. Holly       2014-02-12
  Anna Dillinger                  Newbie          Mt. Holly       2014-02-12
  Anna Dillinger                  Newbie          Mt. Holly       2014-02-12
  Jeff Gregory                    Cross Country   Snow Snake      2013-12-23
  Jeff Gregory                    Advanced        Pine Knob       2013-12-12
  Jeff Gregory                    Advanced        Pine Knob       2013-12-12
  Jeff Gregory                    Advanced        Pine Knob       2013-12-12
  Jeff Gregory                    Advanced        Pine Knob       2013-12-12
  Jeff Gregory                    Intermediate    Pine Knob       2013-12-12
  Jeff Gregory                    Intermediate    Pine Knob       2013-12-12
  Jeff Gregory                    Intermediate    Pine Knob       2013-12-12
  Jeff Gregory                    Intermediate    Pine Knob       2013-12-12
  </code></pre>