performance difference between pgsql and SQL

Hi,

I am using postgreSQL 7.3.4

I have a single table in the databasse.

mytable(id, tag, parent, label)
all in int8.

hash index is built for id and btree index for all attributes.

now, I have over 9 million tuples in the table.

The problem is when I access the database through
psql interface, where I issued the following query:

select tag from mytable where id = 1;

it took 51880 milliseconds to execute.

the "explain" command showed it used seq scan.

I turned enable_seqscan and enable_nestloop off, and it still
used seqscan.

however, if I call it through a pgsql function, it only took
aobut 0.17 milliseconds.

create function test_tag(int8) returns int8 as'
declare
begin
return tag from mytable where id = $1;
end;
' language 'plpgsql';

This looks like a bug to me.
--
Bill Shui