title: PostgreSQL: operator does not exist: timestamp without time zone == timestamp without time zone
body: <p>I have created below trigger and function for update on function where I want to exclude trigger execution when there are update on two columns 'frm' and 'upto' which are of type  "timestamp without time zone"</p>
  
  <p>In trigger function I am checking for updates on these two columns</p>
  
  <pre><code>CREATE OR REPLACE FUNCTION ff() RETURNS TRIGGER AS $$
  BEGIN 
      if((old."frm" == New."frm") and (old."upto" == New."upto") ) then
          insert into TG_TABLE_NAME (select * from inserted );
          New."from" := old."from"; 
          NEW."upto" := current_timestamp;
          RETURN NEW; 
      END IF;
      RETURN NULL;
   END $$ LANGUAGE plpgsql;
  
  create trigger update_trig2 after update on dd 
  for each row execute procedure ff();`
  </code></pre>
  
  <p>After running update query i am getting below error in postgreSQL</p>
  
  <blockquote>
    <p>ERROR:  operator does not exist: timestamp without time zone == timestamp without time zone</p>
  </blockquote>