On Mon, 6 Jan 2014 11:38:32 -0500, Ann Harrison <a...@qbeast.net> wrote: > The FIRST keyword was added to Firebird's SQL in version 1.0 or 1.1 - > in 2000 0r 2001, but the use of FIRST in InterBase goes back much further. > It was part of GDML - and it's purpose was to signal that the query should > be optimized to walk the index (navigate, in the internals) rather than > create > a bitmap and access records in storage order. There's no reason to limit > the number of record a query returns - when you've seen enough, just close > itt. The semantic significance of FIRST and its relatives is "I want the > first > records quickly."
As I see it, optimizer hints are a different beast from limiting the result set using FIRST. The first is a way to influence decisions of the optimizer, and the second describes what is to be delivered (number of rows; which might have a default optimizer behavior, which might be overridden by an optimizer hint(!)). I'd prefer a generic (and 'extensible') way for optimizer hints, because we are currently discussing 'first n rows' only, but that isn't the only possible optimization that could be added. See for example the way SQL Server hints work as I posted in an earlier mail. > So, historically, no, it's neither a workaround nor a hack. Parsing SQL > comments ... that sounds like a hack to me. Adding yet another > non-standard keyword when one already exists and does what you want > doesn't appeal all that much either. Yes, using comments might be a hack. But it provides a separation between describing what you want, and providing the optimizer with hints on how you think it might choose a better plan, and it doesn't 'pollute' the statement syntax. Mark ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349831&iu=/4140/ostg.clktrk Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
