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Creating Oracle partitioned table

Posted on 2012-04-02
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Last Modified: 2012-04-11
I need to create a partition table that will have a Hash partition on batch_id .. Have a question..

Here is the table creation command that I plan to use:

CREATE TABLE mytab1
   (BATCH_ID NUMBER DEFAULT -1,
     ID number NUMBER(*,0),
     Field1 varchar2(10)
)
   PARTITION BY HASH(BATCH_ID)
STORE IN (MyTablespaceName1);


Is this a correct command to create the partitioned  table on BATCH_ID? The table gets created as above.

Does it create multiple partitions for separate group of  BATCH_ID values when they are inserted into the table?
Thank you...
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Question by:toooki
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Christoffer Swanström earned 500 total points
ID: 37797814
You should add the number of partitions you want, e.g.:

CREATE TABLE mytab1
   (BATCH_ID NUMBER DEFAULT -1,
     ID number NUMBER(*,0),
     Field1 varchar2(10)
)
   PARTITION BY HASH(BATCH_ID) PARTITIONS 64
STORE IN (MyTablespaceName1);

If you don't include that you will get only 1 partition (not much of a partitioning...)
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Author Comment

by:toooki
ID: 37797893
Thanks a lot. Ok if I use PARTITIONS 64

I wanted to know if the table has 100 different BATCH_ID values, does it still create only 64 partitions at the max? so there are multiple rows in the table with same BATCH_ID values that reside in the same partition?

Thank you.
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Expert Comment

by:Christoffer Swanström
ID: 37798068
Yes, it will only create the number of partitions you define. Typically you will have lots of distinct key values for each partition.
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Expert Comment

by:Bajwa
ID: 37800958
You will have as many partitions as distinct value of batch_id
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Expert Comment

by:Christoffer Swanström
ID: 37800993
Bajwa: that's not correct. If you do not specify the number of partitions, you will get one partition only, no matter how many distinct values you have for the the column that the table is partitioned on. If you specify the number of partitions, you will get exactly the number of partitions you specified, no more nor less.

You can verify the number of partitions you get when you do not specify the PARTITIONS clause by running the following:

DROP TABLE swc_tst;
CREATE TABLE swc_tst (
col1 NUMBER
)
PARTITION BY HASH(col1)
;

SELECT * FROM all_tab_partitions WHERE table_name = 'SWC_TST';

INSERT INTO SWC_TST VALUES(1);
INSERT INTO SWC_TST VALUES(2);
INSERT INTO SWC_TST VALUES(3);
INSERT INTO SWC_TST VALUES(4);
INSERT INTO SWC_TST VALUES(5);
COMMIT;

SELECT * FROM all_tab_partitions WHERE table_name = 'SWC_TST';

You still have only one partition after inserting multiple values...
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Author Comment

by:toooki
ID: 37835255
Thanks a lot!! I now understand.
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