Oracle: Partition by List – Example

The following post will walk you trough an exercise of creating a partitioned table, using the list partitioning, populating and testing the partition pruning.

Please note I will also post the scripts at the end of the post, so you can download to replicate the work.

Creating our Work Table:

I’m creating a sample table T1 with 4 columns, with the following structure:

SQL:

create table 
 t1
(c1 char(3) not null
, c2 date
, c3 number
, c4 varchar2(100))
partition by list (c1)
 (
 partition ACB values ('ABC')
 , partition ACD values ('ACD')
 )
;

We want to partition this table by the C1 column, which is more, what i call, a Category column: not null, splitting the data into a couple of finite categories. In our case we have 2 categories: ‘ABC’ and ‘ACD’:

I’m generating a sample data set of about 400 000 rows, in this particular case, evenly split between the two partitions.

And afterwards, please note a very important step, I’m gathering my stats 🙂

insert into t1 
select 
 case 
 when mod(level,20) <11 then 'ABC'
 when mod(level,20) >10 then 'ACD'
 end as c1
 , sysdate+level/24
 , level
 , 'test record '||level
from dual
connect by level <=400000;


commit;

execute dbms_stats.gather_table_stats(user,'T1');

Partition Pruning:

Now, let’s run a couple of test to see  how partition is actually helping our performance.

Please note that i used “Autotrace” to show the actual plan and the partition pruning for our selects.

First scenario:

select * from t1;

This is our base test: select all data from our partitioned table:

Second scenario:

select * from t1
where c1='ABC';

or

select * from t1
where c1='ACD';

Filtering on one of the values of the partition key, ‘ABC’:

Third scenario:

select * from t1
where c1 in ('ABC', 'ACD');

Filtering on both values of our partition key (‘ABC’ and ‘ACD’):

Conclusions:

I’ve been using the SQLDeveloper Autotrace to demonstrate the partition pruning.

As you can see, the selects will do partition pruning when filtering on one or multiple partitions.

Scripts:

test-scripts

Please note scripts are uploaded as PDFs but you can still copy the code in.