Oracle-L: Re: Foreign key indexes on individual columns or multiple columns

From: <Jared.Still_at_radisys.com>
Date: Tue, 14 Jan 2003 10:55:25 -0800
Message-ID: <F001.0052F791.20030114105525@fatcity.com>

The only requirement for indexes to support an FK is that the leading columns of the index match the columns of the FK.

I believe that they must also be in the same order, but I'll let you look that up in the fine manual.

So, if you find that you need an index made up of the columns RESP_PARTY_NAME,
CUSTIMER_MOT_ID and FROM_EVENT, the following index would prevent locking:

create index benchmark_hdr_custresp_idx on benchmark_hdr (

   RESP_PARTY_NAME
  ,CUSTIMER_MOT_ID
  , FROM_EVENT
);

There's no need for a separate index on just the FK columns.

HTH Jared

"Krishnaswamy, Ranganath" <Ranganath.Krishnaswamy_at_blr.hpsglobal.com> Sent by: root_at_fatcity.com
01/14/2003 02:29 AM
Please respond to ORACLE-L

        To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
        cc: 
        Subject:        Foreign key indexes on individual columns or multiple columns

Hi List,

                 I have a table by name Benchmark_hdr with the following

columns:

  BENCHMARK_HDR_ID    NUMBER        NOT NULL 
  CALENDAR_TYPE     CHAR (1), 
  UOM               VARCHAR2 (10), 
  CALENDAR_PORT     CHAR (1), 
  CUSTOMER_MOT_ID   NUMBER        NOT NULL 
  RESP_PARTY_NAME   VARCHAR2 (10), 
  FROM_EVENT        NUMBER, 
  TO_EVENT          NUMBER, 
  LAST_UPDATED      DATE

I have created foreign key constraints using the below commands:

  ALTER TABLE BENCHMARK_HDR ADD CONSTRAINT BENCHAMRK_HDR_CUSTOMERESP_FK FOREIGN KEY (RESP_PARTY_NAME, CUSTOMER_MOT_ID)   REFERENCES XM.CUSTOMER_RESPONSIBLE_PARTY (RESP_PARTY_NAME, CUSTOMER_MOT_ID) ; ALTER TABLE BENCHMARK_HDR ADD CONSTRAINT BENCHAMRK_HDR_CUSTOMEREVENT_FK FOREIGN KEY (FROM_EVENT)
  REFERENCES XM.CUSTOMER_EVENT (CUSTOMER_EVENT_ID) ON DELETE CASCADE; ALTER TABLE BENCHMARK_HDR ADD CONSTRAINT BENCHMARK_HDR_CUSTOMEREVENT_FK FOREIGN KEY (TO_EVENT)
  REFERENCES XM.CUSTOMER_EVENT (CUSTOMER_EVENT_ID) ON DELETE CASCADE;   The foreign keys need to be indexed so that the child table is not locked
when a record in the parent table is being updated or deleted. If the foreign keys are indexed the corresponding child record or records are only
locked when the parent table record is being updated or deleted. In this context I would like to seek the advice of the list as to whether I should create indexes on individual foreign keys or should I create one or more composite index(es) on foreign keys? If I need to create a composite index
on which columns should I base my index on? Could anybody advise me on this
with the reasons for following that particular approach? Any help in this regard is very much appreciated.

Thanks and Regards,

Ranganath

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Author: Krishnaswamy, Ranganath
INET: Ranganath.Krishnaswamy_at_blr.hpsglobal.com

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