title: Dropping column in Postgres on a large dataset
body: <p>So I have a table with a large dataset and this table has a three columns that I would like to drop.<br>
  The question is: how will Postgres deal with it?</p>
  
  <p>Will it walk through every entry or will it just update mapping info without much overhead?
  Can I just make an <code>ALTER TABLE</code> or should I use swap-table in this particular case?</p>
  
  <p>And, if it makes any difference, all three columns have fixed length (two integers and one numeric).</p>
  
  <p>I'm sorry if it's been asked already, but Google couldn't find any related questions / articles ...</p>