RE: ** ordered use_nl question

Gints,
  Thanks for your help. I used leading hint and it is working. I assume there is no problem with using it. Thanks again. It was of great help.

  Jonathan/Wolfgang,

     Yes. Thanks for your help. The hint is working same for me with or wihout the comma. I have four tables. I would like one of them to be the beginning table. I was able to do it using leading hint as follows. I will try implement histogram. Thanks

  /*+ leading (b) use_nl(a) */   

It is much faster with this. I am still doing full table scan on table b. I assume histogram will take care of it since earlier it was doing index scan on less selective index.   

Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote:   

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

Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html

Date: Mon, 19 Jun 2006 12:03:15 -0700
From: Wolfgang Breitling

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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