what`s the meaning of CONCATENATION in the explaintext of a Query

From: Volker Graubaum <volker_at_dund-land.de>
Date: Thu, 21 Mar 2002 14:25:42 +0100
Message-ID: <3C99DF56.7A4DBC69@dund-land.de>

Hi,

I`ve a problem with an query.

When I watched in the explaintext off the query, I get very high cost.

SELECT STATEMENT Optimizer=CHOOSE (Cost=3330585440079260 Card=1417602875443650000 Bytes=76550555273957100000)   CONCATENATION
    MERGE JOIN (CARTESIAN) (Cost=20702 Card=83193 Bytes=4492422)

      MERGE JOIN (CARTESIAN) (Cost=11375 Card=83201 Bytes=3411241)
        TABLE ACCESS (FULL) OF SW_REF (Cost=2015 Card=83210
Bytes=2080250)
        SORT (JOIN)
          TABLE ACCESS (FULL) OF ACCOUNT_CONTACT (Cost=7214 Card=3032483
Bytes=48519728)
      SORT (JOIN)
        TABLE ACCESS (FULL) OF ACCOUNT (Cost=7120 Card=3030499

Bytes=39396487)

    HASH JOIN (Cost=20702 Card=83193 Bytes=4492422)

      HASH JOIN (Cost=11375 Card=83201 Bytes=3411241)
        TABLE ACCESS (FULL) OF SW_REF (Cost=2015 Card=83210
Bytes=2080250)
        TABLE ACCESS (FULL) OF ACCOUNT_CONTACT (Cost=7214 Card=3032483
Bytes=48519728)
      TABLE ACCESS (FULL) OF ACCOUNT (Cost=7120 Card=3030499

Bytes=39396487)

How can this happend, and what is the meaning of CONCATENATION? Normally I won`t start an Query which cost about 100000 or more, but this???

Below you will find the query, hope that you can help me.

thx and greetings Volker

  select a.account_id,a.account_contact_id, a.kundenum , b.MOOD, b.CHANGE_DT, c.ACCT_LOCATION_ID, c.FIRST_NAME   from sw_ref a, account b, account_contact c   where a.ACCOUNT_ID = b.ACCOUNT_ID

        and
            a.ACCOUNT_CONTACT_ID = c.ACCOUNT_CONTACT_ID
        and
           (a.kundenum_aktiv is null and a.rolle = 'DEBS') or

(a.kundenum_aktiv
<> 'N' and a.rolle = 'DEBS')
Received on Thu Mar 21 2002 - 07:25:42 CST