Message-ID: <3F4228ED.2962F13F@st.com>
Date: Tue, 19 Aug 2003 15:41:01 +0200
From: Marco Vezzoli <marco.vezzoli@st.com>
MIME-Version: 1.0
To: tgl@sss.pgh.pa.us
Cc: pgsql-sql@postgresql.org
Subject: Re: postgres 7.1.3: why does the query plan ignore indexes?
References: <3F41E343.AE3B5E@st.com> <27563.1061299589@sss.pgh.pa.us>
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tgl@sss.pgh.pa.us wrote:
> 
> Marco Vezzoli <marco.vezzoli@st.com> writes:
> > ewsweb_test=> \d measures_product
> > Index "measures_product"
> >  Attribute  |   Type
> > ------------+----------
> >  product_id | smallint
>                 ^^^^^^^^
> 
> > ewsweb_test=> explain select zero_yield, gross from measures where
> > product_id=29 and date between '2003-03-12' and '2003-08-14';
>   ^^^^^^^^^^^^^
> 
> "29" is taken as an integer (int4).  To get an indexscan on an int2
> column, you need to explicitly cast it to int2:
>         product_id = 29::smallint
> or you can put it in quotes and let the parser figure out the right
> type:
>         product_id = '29'
> 
> Yes, we'd like to make this better, but there are surprisingly many
> pitfalls in tinkering with the assignment of datatypes to constants...
> 
>                         regards, tom lane
> 
> PS: you could also consider whether it's really saving you any space to
> store product_id as a smallint instead of int.  Because of alignment
> considerations, it very possibly isn't.

thank you, now it works better; however it seems that the date index is
ignored.

ewsweb_test=> explain select zero_yield, gross from measures where
product_id=29::smallint and date between '2003-03-12' and '2003-08-14';
NOTICE:  QUERY PLAN:

Index Scan using measures_product on measures  (cost=0.00..3792.27
rows=254 width=12)

EXPLAIN

-- 
Marco Vezzoli	   tel. +39 039 603 6852
STMicroelectronics fax. +39 039 603 5055