Slow Query problem

Dear All,
 
I am currently using PostgreSQL database version 8.0.13.  My problem relates to a slow result when a query using a defined view joins to another table for a result.
 
Background:  I have 7 tables of invoice transactions.  The tables are slightly different in that they record different data (some different columns in each table).  There are about 250,000 records when a union view is created.  A simply query on this union performs satisfactorily.

 

The invoice table union view is then joined with a table of receipts (which have a total of about 150,000 records). 

 

It takes around 3.5 seconds for "select * from view_transaction where member_id = 999  and receipt_no is null" (which returns unpaid invoices).

 

By hard coding I created a single table from the 7 invoice tables (instead of creating a union) and then used it with receipt table.  This time for the same query improved to 1.8 seconds.

 

To further improve things I tried to code the selection rather than to use a view, and so "select * from temp_transaction where member_id = 999 and receipt_no is null" provided the result in .5 second. (2 records returned containing the details of receipt_no, transaction_no, transaction_type, transaction_amount, member_id).

 

I would prefer to be able to have completed the above by using unions and views.  Is it possible to do this, or am I better creating a permanent table of invoices and writing the query as I did above?

 

Any comments on this and suggestions would be appreciated.  If there is documentation where I can read up please let me have a link.
 
Thank You,
 
Premsun