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

Marco Vezzoli <marco(dot)vezzoli(at)st(dot)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.