On Wed, May 20, 2009 13:07, James B. Byrne wrote:
> This seems to be working. I had to take a different approach as I
> had misapprehended GROUP BY completely.
>
>
> SELECT *
> FROM currency_exchange_rates AS xchg1
> WHERE id
> IN (
> SELECT id
> FROM currency_exchange_rates as xchg2
> WHERE
> xchg1.currency_code_base = xchg2.currency_code_base
> AND
> xchg1.currency_code_quote = xchg2.currency_code_quote
> ORDER BY currency_code_base,
> currency_code_quote,
> effective_from DESC
> LIMIT 1 )
> ORDER BY currency_code_base,
> currency_code_quote,
> effective_from DESC
Looking at this I have to wonder what will be the effect of having
tens of thousands of rate-pairs on file. Would this query be
improved by first doing a sub-query on base/quote pairs that
returned DISTINCT pairs and then do the IN condition using that?
--
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James B. Byrne mailto:ByrneJB@Harte-Lyne.ca
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