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" <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
01/14/2003 02:29 AM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
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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