title: Cannot create non existing column in SQL database
body: <p>I'm executing the following query on my db:</p>
  
  <pre><code>alter table Client drop column "IsVersionValid"
  GO
  alter table Client add "IsVersionValid" bit NULL
  </code></pre>
  
  <p>with the following result:</p>
  
  <p>Msg 4924, Level 16, State 1, Line 1
  ALTER TABLE DROP COLUMN failed because column 'IsVersionValid' does not exist in table 'Client'.
  Msg 2705, Level 16, State 6, Line 3
  Column names in each table must be unique. Column name 'IsVersionValid' in table 'Client' is specified more than once.</p>
  
  <p>How is this possible? I'm trying to add a column that is not existing in my table. I tried doing this manually via the table designer of ssms. But this gives te same result.</p>