title: select * vs select column
body: <p>If I just need 2/3 columns and I query <code>SELECT *</code> instead of providing those columns in select query, is there any performance degradation regarding more/less I/O or memory?</p>
  
  <p>The network overhead might be present if I do select * without a need.</p>
  
  <p>But in a select operation, does the database engine always pull atomic tuple from the disk, or does it pull only those columns requested in the select operation?</p>
  
  <p>If it always pulls a tuple then I/O overhead is the same.</p>
  
  <p>At the same time, there might be a memory consumption for stripping out the requested columns from the tuple, if it pulls a tuple.</p>
  
  <p>So if that's the case, select someColumn will have more memory overhead than that of select *</p>