title: Remove specific columns using Azure Data Factory
body: <p>I have set of files in ADLS. Number of columns varies in each file.</p>
  <p>File 1 will have the columns : Row_Number, Col_A, Col_B, null</p>
  <p>File 2 will have the columns : Row_Number, Col_1, Col_2, Col_3 , null</p>
  <p>File 3 will have the columns : Row_Number, Col_A1, Col_A2, null</p>
  <p>There will be more than 50 files in my ADLS.
  I would need to remove first and last column in each file or to be specific , I need to remove columns which has columns names as Row_Number and null.</p>
  <p>Can any help me what should be my expressions in Derived column / Select.</p>
  <p>Thanks for your help.</p>