RE: ** ordered use_nl question

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Tue, 20 Jun 2006 07:41:32 +0100
Message-ID: <00bc01c69434$919c55f0$0300a8c0@Primary>

Wolfgang,

The comma in use_nl (a,b,c,d) is allowed
(at least in some versions of Oracle) even
though it may not be expected.

The interpretation of the hint is that it is simply a shorthand for

    use_nl(a)
    use_nl(b)
    use_nl(c)
    use_nl(d)

I think it would be quite helpful if the OP posted the original SQL, showing us the
actual use of hint. There is no reason for Oracle to ignore something like
 /*+

      ordered
      use_nl(t1, t4, t2, t3)

 */
if its use is valid.

See you in Zurich this evening.

Regards

Jonathan Lewis
http://www.oracle.com/technology/community/oracle_ace/ace1.html#lewis

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

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Date: Mon, 19 Jun 2006 12:03:15 -0700
From: Wolfgang Breitling <breitliw_at_centrexcc.com> Subject: RE: ** ordered use_nl question

The syntax is still not right. Read the documentation (as I did): No comma in the list within the use_nl hint. Also, according to the documentation, the table
(s) listed in the hint "is the name or alias of a table to be used as the inner
table of a nested loops join". I know that a list is legal, I just don't know what that is supposed to mean in terms of being the inner table in an NL join. I always use a single alias in the use_nl hint, except I hardly use such hints at all. If the selectivity of the predicate used to select the driving table in the current plan, maybe a better approach would be to collect a histogram so that the optimizer "knows" that.

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Received on Tue Jun 20 2006 - 01:41:32 CDT