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? -- *** E-Mail is NOT a SECURE channel *** James B. Byrne mailto:byrn...@harte-lyne.ca Harte & Lyne Limited http://www.harte-lyne.ca 9 Brockley Drive vox: +1 905 561 1241 Hamilton, Ontario fax: +1 905 561 0757 Canada L8E 3C3 -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
