If "$hist_plan_prolog_1" is a table name, and NOT a perl variable, the best bet is to use non-interpolating single quotes, and NOT escape the $.

But the query would be more readable if you used "heredoc" syntax.

here is a sample I use:

   my $sql=<<"_SQL_";
    SELECT cl_plugins.pid_number as pid, plugin_catalog.pid AS plugin_
+name,
       plugin_catalog.description AS name, plugin_catalog.version, bui
+ld
    FROM cl_plugins, plugin_catalog
    WHERE     cl_plugins.cid::text     = '$proxy->{CID}'
          AND cl_plugins.pid_number    = plugin_catalog.pid_number
          AND cl_plugins.version::text = plugin_catalog.version::text;
_SQL_
[download]

In my case, I DO use interpolation, and the string does expand the reference to $proxy->{CID}.

Your query could be:

my $sql=<<"__SQL__";
SELECT 
  to_char(pp.SUBMITTIME, 'YYYY-MM-DD HH:MM:SS') SUBMITTIME,
  to_char(pp.QUEUETIME, 'YYYY-MM-DD HH:MM:SS') QUEUETIME,
  to_char(pp.PREPTIME, 'YYYY-MM-DD HH:MM:SS') PREPTIME,
  to_char(pp.STARTTIME, 'YYYY-MM-DD HH:MM:SS') STARTTIME,
  pp.SESSIONID, pp.PLANID 
from '\$hist_plan_prolog_1' pp
where pp.SUBMITTIME between '2014-06-26 05:00' and '2014-06-26 08:00:0
+0' 
order by pp.SUBMITTIME
__SQL__
[download]

This allows for the potential introduction of perl variables, where you would NOT escape the $.