'Expensive' column in result set

Hi all,

I have a select that involves a column in the result set that is expensive to get.
I need to use the expensive column in a subsequent calculated column.

Is there a syntax to run the expensive function once only or does it just have to be done,
blk_speed() is the expensive function.

Example of what I would like to do, does not work of course:
select
    b.block,
    b.p_code,
    p.description,
    p.blk_speed as "set",
    blk_speed( b.block ) as "actual",
    actual / set * 100 as "Speed %"
from block b, product p
where b.p_code = p.p_code;

This does work
select
    b.block,
    b.p_code,
    p.description,
    p.blk_speed as "set",
    blk_speed( b.block ) as "actual",
    blk_speed( b.block ) / ( p.blk_speed + 0.0001 ) * 100 as "Speed %"
from block b, product p
where b.p_code = p.p_code;

OR is postgres smart enough to know it only needs to get blk_speed() once.

Thanks

Allan


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