How to drop multiple interval partitions based on date? - oracle

Question

I have a table based on daily partitions.
I can drop a paritition using the below query
ALTER TABLE MY_TABLE DROP PARTITION FOR(TO_DATE('19-DEC-2017','dd-MON-yyyy'))
How can I drop all the partitions (multiple partitions) before 15 days?

Answer 1

You can use PL/SQL like this.
DECLARE
CANNOT_DROP_LAST_PARTITION EXCEPTION;
PRAGMA EXCEPTION_INIT(CANNOT_DROP_LAST_PARTITION, -14758);
ts TIMESTAMP;
BEGIN
FOR aPart IN (SELECT PARTITION_NAME, HIGH_VALUE FROM USER_TAB_PARTITIONS WHERE TABLE_NAME = 'MY_TABLE') LOOP
EXECUTE IMMEDIATE 'BEGIN :ret := '||aPart.HIGH_VALUE||'; END;' USING OUT ts;
IF ts < SYSTIMESTAMP - INTERVAL '15' DAY THEN
BEGIN
EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE DROP PARTITION '||aPart.PARTITION_NAME|| ' UPDATE GLOBAL INDEXES';
EXCEPTION
WHEN CANNOT_DROP_LAST_PARTITION THEN
EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE SET INTERVAL ()';
EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE DROP PARTITION '||aPart.PARTITION_NAME;
EXECUTE IMMEDIATE 'ALTER TABLE MY_TABLE SET INTERVAL( INTERVAL ''1'' DAY )';
END;
END IF;
END LOOP;
END;

Answer 2

For interval partitioned tables (that you probably use based on the exception ORA-14758) you may profit from using the partition_extended_name syntax.
You need not know the partition name, you reference the partition with a DATE, e.g.
alter table INT_PART drop partition for (DATE'2018-09-01')
So to drop your last 15 partitions starting with the current day this loop is to be performed:
declare
v_sql VARCHAR2(4000);
begin
for cur in (select
trunc(sysdate,'MM') - numtodsinterval(rownum - 1, 'day') my_month
from dual connect by level <= 15)
loop
v_sql := q'[alter table INT_PART drop partition for (DATE']'||
to_char(cur.my_month,'YYYY-MM-DD')||q'[')]';
execute immediate v_sql;
end loop;
end;
/
You must use execute immediateas the DATEin the ALTER TABLE statement must by static.
Following statements are generated and executed:
alter table INT_PART drop partition for (DATE'2018-09-01')
alter table INT_PART drop partition for (DATE'2018-08-31')
....
alter table INT_PART drop partition for (DATE'2018-08-19')
alter table INT_PART drop partition for (DATE'2018-08-18')
Additional to the exception ORA-14758 (that I ignore - see the note below) you should handle the exception
ORA-02149: Specified partition does not exist
dependent on you business this should be probably ignored - for this day no partition exists (and you will never reference this day using the partition dictionary metadata).
Note to workaround the ORA-14758 Last partition in the range section cannot be dropped exception you may use this little trick.
I create a dummy partition (without an extent) called P_MINVALUE that plays the role of the interval start in the far past and it will therefore never be dropped.
CREATE TABLE int_part
(
transaction_date TIMESTAMP not null,
vc_pad VARCHAR2(100)
)
SEGMENT CREATION DEFERRED
PARTITION BY RANGE (transaction_date) INTERVAL (NUMTODSINTERVAL(1,'DAY'))
(
PARTITION P_MINVALUE VALUES LESS THAN (TO_DATE('2000-01-01', 'YYYY-MM-DD') )
);