Dmitry,
> > Right. And if you want to give the optimizer a hint that it should choose
> > the second plan, change the query like this:
> >
> > select first 1000000 * from MOVIES where COMMENTS like '%yacht% order
> > by NAME;
> >
> > If you think your client may want more than a million rows, increase
> > that number.
>
> I mentioned this approach in my initial message and it does not look
> good to me. I treat it as a workaround / hack, not a solution.
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.
> Also, there may be (in fact, there are) customers who need the FIRST
> ROWS strategy being the default one. And rewriting a majority of their
> queries to include the dummy FIRST clause is not something they can
> consider seriously.
>
So would you consider a connection option? A transaction option?
Best regards,
Ann
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