title: PostgreSQL column type conversion from bigint to bigserial
body: <p>When I try to change the data type of a column in a table by alter command...</p>
  
  <pre><code>alter table temp alter column id type bigserial;
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>ERROR:  type "bigserial" does not exist
  </code></pre>
  
  <p>How can I change the datatype from bigint to bigserial?</p>