title: sql server table restriction on two fields
body: <p>I have a table with multiple columns with data periodically inserted. I would like to focus on two fields where if one value is entered in Column A, nothing should be allowed to be entered in column B. Hope this makes sense; I will illustrate below:</p>
  
  <pre><code>TABLE TEST
  COLUMN a
  COLUMN b
  COLUMN c 
  DATEADDED
  
  INSERT INTO TEST(COLUMN A, COLUMN B)
  VALUE('HELLO','HELLO')
  </code></pre>
  
  <p>This should not be allowed to occur but rather a null value should be in either one. Basically a constraint to restrict one value being in either column for a given record.</p>