FIRST_ROWS would seem to imply just that: return the
first row to me as fast as possible. The optimizer
will do this via indexes, hash joins, full table scan,
anti joins, whatever it deems to be the fastest.
The methods I mentioned may not even be considered
by the optimizer, I am not privy to its internals.
The INDEX hint ( without specifying an index ) will consider
all of the indexes, choose one, or maybe even merge the
results from several indexes. It will not even consider
doing a full table scan.
This is all available of course, in the 'Tuning for Performance'
Oracle manual.
Jared
On Tue, 20 Feb 2001, dana mn wrote:
>
> Is there any difference between the FIRST_ROWS hint
> (which is said to "generally force the use of indexes" - Niemiec)
> and the use of the INDEX hint (without specifying a particular
> index)?
>
> Is something else going on behind the scenes with FIRST_ROWS or is this
> gratuitous bloat that shouldn't be in the optimizer? (or a placeholder
> for future innovation)?
>
> Thanks very much.
>
> - Dana
>
>
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