On 2017/09/14 7:10 PM, Simon Slavin wrote:
On 14 Sep 2017, at 5:55pm, R Smith <rsm...@rsweb.co.za> wrote:
Richard, wouldn't it be possible to supply a wrapping function (perhaps a hint
function, like the likelihood() function), that takes another function as a
parameter and then ensuring that THAT gets calculated only once?
Can you not do it with WITH ? I don’t really understand how WITH works but it
would seem to evaluate its terms just once for each iteration.
I think that's actually one of the things one of the posters tried and
found not to work. The problem is the WITH syntax in theory is just-like
constructing a temporary table and using the values from there, but in
reality (AFAIK) it's just a mathematical construct that re-routes the
query, so anything that is a parameter to a function (or a function
itself) in the WITH clause gets re-evaluated every time the main query
refers to the WITH table.
Perhaps if you can force the WITH into building an in-memory table with
the results from, say a recursive function, it would indeed be a
possibility, but I'm pretty sure that isn't a possibility. This is
something easily done by the bigger engines since they rarely need to
concern themselves with memory limitations, but then, for that same
reason, they can (and do) just implement CSE without much fuss.
I was trying to posit a light-weight approach that puts a bit of onus on
the programmer, but still answers the need - but no solution to this
will be "quick and easy".
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