Okay, I've got two queries that I think the planner should reduce to be 
logically equivalent but it's not happening. The example queries below have 
been simplified as much as possible while still producing the problem. 

What I'm trying to do is create a single prepared statement that can handle 
null parameters rather than have to dynamically generate the statement in my 
app code based on supplied parameters.

Basically the date constants below would be substituted with parameters 
supplied on a web search form (or nulls).


Here is the query and EXPLAIN that runs quickly:
  SELECT case_id FROM case_data 
  WHERE case_filed_date > '2004-09-16' 
    AND case_filed_date < '2004-09-20'

                       QUERY PLAN
-------------------------------------------------------------
Index Scan using case_data_case_filed_date on case_data  
(cost=0.00..13790.52 rows=3614 width=18)
  Index Cond: ((case_filed_date > '2004-09-16'::date) 
           AND (case_filed_date < '2004-09-20'::date))


And here is the query and EXPLAIN from the version that I believe the planner 
should reduce to be logically equivalent:
 SELECT case_id FROM case_data 
 WHERE (('2004-09-16' IS NULL) OR (case_filed_date > '2004-09-16'))
   AND (('2004-09-20' IS NULL) OR (case_filed_date < '2004-09-20'))

                       QUERY PLAN
-------------------------------------------------------------
Seq Scan on case_data  (cost=0.00..107422.02 rows=27509 width=18)
  Filter: ((('2004-09-16' IS NULL) OR (case_filed_date > '2004-09-16'::date))
       AND (('2004-09-20' IS NULL) OR (case_filed_date < '2004-09-20'::date)))


I was hoping that the null comparisons would get folded out by the planner 
relatively cheaply. But as you can see, the first query uses indexes and the 
second one uses sequence scans, thereby taking much longer.  I guess my 
question is - is there a better way to accomplish what I'm doing in SQL or am 
I going to have to dynamically generate the statement based on supplied 
parameters?

Thanks,
Ryan

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