Re: postgres 7.1.3: why does the query plan ignore indexes?

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

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