Re: sequence of numbers

From: Connor McDonald <hamcdc_at_yahoo.co.uk>
Date: Mon, 19 Nov 2001 06:14:43 -0800
Message-ID: <F001.003C866F.20011119045016@fatcity.com>

Maybe something like:

select /*+ INDEX(a mt_ix) */ *
from mt a
where mt1 > 0
and not exists
  ( select null
    from mt
    where mt1 = a.mt1+1)
and rownum = 1

where 'mt_ix' is the index on MT1. This should work ok as long as the number is anticipated to be toward the lower end of the range. For example, I ran it on a 5 million row table (~6500 blocks), on my pc:

looking for value: 4999
time: <1sec

looking for value: 4000000
time: 2 mins

hth
connor

• Jan Pruner <jan_at_pruner.cz> wrote: > Hello,
  > I've a table mt ( mt1 NUMBER(10) NOT NULL ) with
  > unique index on the mt1
  > column.
  > There's a sequence of numbers 1,2,3,4,6,7,8,10,11
  > ... in the mt1
  >
  > Now, I want to get the smallest number which is not
  > in mt1
  > (excluding min(mt1)-x of course) into XY (in my
  > example is it n. 5).
  >
  > When I use SELECT MIN(mt1)-1 INTO XY FROM MT WHERE
  > MT1 NOT IN (select mt1+1
  > from mt)
  > my perfromance goes pretty down :-))) (there's
  > about 5 mil. of numbers).
  >
  > Some idea how to get it without cursor?
  >
  > Thanks (and sorry it's monday)
  > JP
  > --
  > Please see the official ORACLE-L FAQ:
  > http://www.orafaq.com
  > --
  > Author: Jan Pruner
  > INET: jan_at_pruner.cz
  >
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Connor McDonald
http://www.oracledba.co.uk (mirrored at http://www.oradba.freeserve.co.uk)

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Received on Mon Nov 19 2001 - 08:14:43 CST