How to SELECT RDBMS data for different values of Partition column - sql

Question

I have an Oracle table as below:
CREATE TABLE "TABLE1"
(
"TABLE_ID" VARCHAR2(32 BYTE),
"TABLE_DATE" DATE,
"TABLE_NAME" VARCHAR2(2 BYTE)
)
PARTITION BY RANGE ("TABLE_DATE")
Guess this table has data partitioned by the TABLE_DATE column.
How can I use this partitioning column to fetch data faster from this table in a WHERE clause like ...
SELECT * FROM TABLE1 PARTITION (P1) p
WHERE p.TABLE_DATE > (SYSDATE - 90) ;

Answer 1

You should change your partitioning to match your queries, not change your queries to match your partitioning. In most cases we shouldn't have to specify which partitions to read from. Oracle can automatically determine how to prune the partitions at run time.
For example, with this table:
create table table1
(
table_id varchar2(32 byte),
table_date date,
table_name varchar2(2 byte)
)
partition by range (table_date)
(
partition p1 values less than (date '2019-05-06'),
partition p2 values less than (maxvalue)
);
There's almost never a need to directly reference a partition in the query. It's extra work, and if we list the wrong partition name the query won't work correctly.
We can see partition pruning in action using EXPLAIN PLAN like this:
explain plan for
SELECT * FROM TABLE1 p
WHERE p.TABLE_DATE > (SYSDATE - 90) ;
select *
from table(dbms_xplan.display);
In the results we can see the partitioning in the Pstart and Pstop columns. The KEY means that the partition will be determined at run time. In this case, the start partition is based on the value of SYSDATE.
Plan hash value: 434062308
---------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
---------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 30 | 2 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE ITERATOR| | 1 | 30 | 2 (0)| 00:00:01 | KEY | 2 |
|* 2 | TABLE ACCESS FULL | TABLE1 | 1 | 30 | 2 (0)| 00:00:01 | KEY | 2 |
---------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("P"."TABLE_DATE">SYSDATE#!-90)
Note
-----
- dynamic statistics used: dynamic sampling (level=2)