Ann Harrison <a...@qbeast.net> писал(а) в своём письме Mon, 06 Jan 2014 20:38:32 +0400:
> 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." > 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. Analysis of comments and its impact on the plan really looks like the hacker way. Enter a keyword for a custom optimizer hints needed in any case. No matter how clever the optimizer it can still be wrong (and it is not only the choice of strategies FIRST / ALL ROWS). Tips exist in one form or another in many RDBMS (Oracle, MS SQL, DB2 ...) -- Написано в почтовом клиенте браузера Opera: http://www.opera.com/mail/ ------------------------------------------------------------------------------ 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
