Repetitive code - Mailing list pgsql-sql

Hi,

This is prompted by the previous thread on "SQL Technique Question".  I 
have the following query, extracted from a PHP script, where $dt is a 
date provided to the script.
    SELECT created, topic_id, 0, 0, 0, 0 FROM topic    WHERE created >= $dt AND page_type IN (1, 2)  UNION    SELECT
updated,topic_id, 1, 0, 0, 0 FROM topic    WHERE date_trunc('day', updated) != created      AND updated >= $dt AND
page_typeIN (1, 2)  UNION    SELECT e.created, subject_id, 0, 1, entry_id, subject_type    FROM entry e, topic    WHERE
subject_id= topic_id AND e.created >= $dt      AND page_type IN (1, 2)  UNION    SELECT e.created, actor_id, 0, 1,
entry_id,actor_type    FROM entry e, topic    WHERE actor_id = topic_id AND e.created >= $dt      AND page_type IN (1,
2) UNION    SELECT e.updated, subject_id, 1, 1, entry_id, subject_type    FROM entry e, topic    WHERE
date_trunc('day',e.updated) != e.created      AND subject_id = topic_id AND e.updated >= $dt      AND page_type IN (1,
2) UNION    SELECT e.updated, actor_id, 1, 1, entry_id, actor_type    FROM entry e, topic    WHERE date_trunc('day',
e.updated)!= e.created      AND actor_id = topic_id AND e.updated >= $dt      AND page_type IN (1, 2)  UNION    SELECT
e.created,e.topic_id, 0, 1, entry_id, rel_type    FROM topic_entry e, topic t    WHERE e.topic_id = t.topic_id AND
e.created>= $dt      AND page_type IN (1, 2)  UNION    SELECT e.updated, e.topic_id, 1, 1, entry_id, rel_type    FROM
topic_entrye, topic t    WHERE e.topic_id = t.topic_id      AND date_trunc('day', e.updated) != e.created      AND
e.updated>= $dt AND page_type IN (1, 2);
 

As you can see, there's quite a bit of repetitive code, so the previous 
thread got me to thinking about simplifying it, perhaps through a view, 
perhaps through the use of CASE statements, particularly since I'm about 
to add at least one other table to the mix.

As background, each table has a 'created' date column and an 'updated' 
timestamp column and the purpose of the various selects is to find the 
rows that were created or updated since the given $dt date.  The third 
expression in each select list is an indicator of NEW (0) or CHANGED 
(1).  The fourth item is a code for row type (topic=0, entry=1, but a 
new code is coming).

I've been trying to figure out if simplifying into a view (one or more) 
is indeed possible.  One factoring out that I can see is the "topics of 
interest" restriction (i.e., the join of each secondary table back to 
topic to get only topics whose page_types are 1 or 2).  Another 
redundancy is the "date_trunc('day', updated) != created" which is there 
to avoid selecting "changed" records when they're actually new. 
However, although creating these views may simplify the subqueries it 
doesn't seem there is a way to avoid the eight-way UNION, or is there?

TIA

Joe