Skip site navigation (1) Skip section navigation (2)

Sequential Scans On Complex Query With UNION - see why this fails

From: Steve Tucknott <steve(at)retsol(dot)co(dot)uk>
To: PostGreSQL <pgsql-novice(at)postgresql(dot)org>
Subject: Sequential Scans On Complex Query With UNION - see why this fails
Date: 2006-01-02 09:10:45
Message-ID: 1136193045.4179.1.camel@retsol1 (view raw or flat)
Thread:
Lists: pgsql-novice

PostgreSql 8.0.3

I have a complex query that I want to read the data in a hierarchical
manner - ie from master table filtered rows to sub set1, from subset1 to
subset2 etc. The query is in the attached file, as is the explain. What
I do not understand is why I get sequential scans on certain tables - ie
the purchaseOrdDet, product, supplierProduct when each of the joins
linking the tables hits a valid 'record number' based index.
The query is trying to find all purchase orders within a period, then
all the lines for those orders, products for those lines etc. The union
selects from the supplierproduct/product tables on both sides - in one
case it uses the index and on the other does a sequential scan.

I am obviously doing something wrong in the structure of the query - any
ideas?

Also,...as a quick 'method' question..when writing embedded joins, which
syntax is easier for the optimiser? Should you do:

FROM table tableA AS A
           JOIN tableB AS B
                    JOIN tableC AS C
                             JOIN tableD AS D
                             ON  C.joinD = D.join
                             JOIN tableE AS E
                              ON c.joinE = E.join
                    ON B.joinC = C.join
           ON A.joinB = B.join

OR
FROM table tableA AS A
           JOIN tableB AS B
           ON A.joinB = B.join
                    JOIN tableC AS C
                    ON B.joinC = C.join
                             JOIN tableD AS D
                             ON  C.joinD = D.join
                             JOIN tableE AS E
                              ON c.joinE = E.join

OR is it immaterial and just a matter of style?

Regards,

Steve Tucknott





Attachment: QUERYPLAN
Description: text/plain (15.2 KB)
Attachment: SQL
Description: text/plain (3.3 KB)

Responses

pgsql-novice by date

Next:From: Frank BaxDate: 2006-01-02 14:49:32
Subject: Re: backup by schema
Previous:From: First LastDate: 2006-01-02 09:09:39
Subject: can't log on to phppgadmin

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group