Oracle dropping last PARTITION for a table - oracle

Question

I'm trying to drop all partitions for a table and I'm running into the following error:
ORA-14083: cannot drop the only partition of a partitioned table ORA-06512:
I know I can drop the table and recreate it but I want to see if my procedure can be modified to use an EXCEPTION that sets the retention to nothing, drops the PARTITION and sets the INTERVAL back to its original value?
Any help and expertise would be greatly appreciated. Below is my test CASE.
CREATE OR REPLACE PROCEDURE ddl(p_cmd varchar2)
authid current_user
is
BEGIN
dbms_output.put_line(p_cmd);
execute immediate p_cmd;
END;
/
CREATE OR REPLACE PROCEDURE
drop_partition(
p_tab varchar2,
p_date date
) authid current_user
is
v_high_value date;
cursor v_cur is
select table_name,
partition_name,
high_value,
partition_position
from user_tab_partitions
where table_name = upper(p_tab);
begin
for v_rec in v_cur loop
execute immediate 'select ' || v_rec.high_value || ' from dual' into v_high_value;
if v_high_value <= trunc(p_date)
then
-- dbms_output.put_line ('partition ' || v_rec.partition_name || ' high value is ' || to_char(v_high_value,'mm/dd/yyyy'));
--ddl( 'ALTER TABLE ' || p_tab || ' DROP PARTITION FOR(DATE ' || TO_CHAR(v_high_value,'YYYY-MM-DD') || ')');
ddl('alter table '||p_tab||' drop partition '||v_rec.partition_name);
end if;
end loop;
END;
/
CREATE TABLE partition_retention
(
seq_num NUMBER GENERATED BY DEFAULT AS IDENTITY (START WITH 1) NOT NULL,
TABLE_NAME VARCHAR2(30),
DAYS NUMBER(6),
CONSTRAINT
partition_retention_pk primary key (table_name));
/
INSERT into partition_retention(TABLE_NAME, DAYS)
WITH data as (
select 'T1', 0
from dual union all
select 'T3', 15
from dual union all
select 'T4', 10
from dual union all
select 'T5', 5
from dual)
SELECT * from data;
/
CREATE TABLE t1 (
seq_num NUMBER GENERATED BY DEFAULT AS IDENTITY (START WITH 1) NOT NULL,
dt DATE
)
PARTITION BY RANGE (dt)
INTERVAL (NUMTODSINTERVAL(7,'DAY'))
(
PARTITION OLD_DATA values LESS THAN (TO_DATE('2022-01-01','YYYY-MM-DD'))
);
/
INSERT into t1 (dt)
with dt (dt, interv) as (
select date '2022-01-01', numtodsinterval(1,'DAY') from dual
union all
select dt.dt + interv, interv from dt
where dt.dt + interv < date '2022-02-01')
select dt from dt;
/
BEGIN
FOR td IN
(
SELECT table_name
, NVL (pr.days, 30) AS days
FROM user_part_tables pt
JOIN user_part_key_columns pkc ON pkc.name = pt.table_name
JOIN user_tab_cols tc USING (table_name, column_name)
LEFT JOIN partition_retention pr USING (table_name)
WHERE pkc.object_type = 'TABLE'
AND pt.partitioning_type = 'RANGE'
AND REGEXP_LIKE (tc.data_type, '^DATE$|^TIMESTAMP.*')
ORDER BY table_name
)
LOOP
drop_partition(
td.table_name,
trunc(sysdate-td.days)
);
END LOOP;
END;
/

Answer 1

Your question says "drop the last partition" which can be different to "drop the only partition"
As stated already in comments, you cannot drop the partition when only one partition is left. If you like to remove the data, then you can TRUNCATE the partition.
This PL/SQL Block should cover all your cases:
CREATE TABLE PARTITION_RETENTION (
TABLE_NAME VARCHAR2(30),
RETENTION INTERVAL DAY(3) TO SECOND(0) --> More generic than number of days
);
DECLARE
CANNOT_DROP_LAST_PARTITION EXCEPTION;
PRAGMA EXCEPTION_INIT(CANNOT_DROP_LAST_PARTITION, -14758);
CANNOT_DROP_ONLY_ONE_PARTITION EXCEPTION;
PRAGMA EXCEPTION_INIT(CANNOT_DROP_ONLY_ONE_PARTITION, -14083);
ts TIMESTAMP;
CURSOR TablePartitions IS
SELECT TABLE_NAME, PARTITION_NAME, p.HIGH_VALUE, t.INTERVAL, RETENTION, DATA_TYPE
FROM USER_PART_TABLES t
JOIN USER_TAB_PARTITIONS p USING (TABLE_NAME)
JOIN USER_PART_KEY_COLUMNS pk ON pk.NAME = TABLE_NAME
JOIN USER_TAB_COLS tc USING (TABLE_NAME, COLUMN_NAME)
JOIN PARTITION_RETENTION r USING (TABLE_NAME);
BEGIN
FOR aPart IN TablePartitions LOOP
EXECUTE IMMEDIATE 'BEGIN :ret := '||aPart.HIGH_VALUE||'; END;' USING OUT ts;
IF ts < SYSTIMESTAMP - aPart.RETENTION THEN
BEGIN
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' DROP PARTITION '||aPart.PARTITION_NAME|| ' UPDATE GLOBAL INDEXES';
DBMS_OUTPUT.PUT_LINE('Dropped partittion '||aPart.PARTITION_NAME ||' from table '||aPart.TABLE_NAME);
EXCEPTION
WHEN CANNOT_DROP_ONLY_ONE_PARTITION THEN
DBMS_OUTPUT.PUT_LINE('Cannot drop the only partittion '||aPart.PARTITION_NAME ||' from table '||aPart.TABLE_NAME);
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' TRUNCATE PARTITION '||aPart.PARTITION_NAME|| ' UPDATE GLOBAL INDEXES';
DBMS_OUTPUT.PUT_LINE('Truncated partittion '||aPart.PARTITION_NAME ||' from table '||aPart.TABLE_NAME);
WHEN CANNOT_DROP_LAST_PARTITION THEN
BEGIN
DBMS_OUTPUT.PUT_LINE('Drop last partittion '||aPart.PARTITION_NAME ||' from table '||aPart.TABLE_NAME);
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' SET INTERVAL ()';
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' DROP PARTITION '||aPart.PARTITION_NAME;
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' SET INTERVAL( '||aPart.INTERVAL||' )';
EXCEPTION
WHEN CANNOT_DROP_ONLY_ONE_PARTITION THEN
-- Depending on the order the "last" partition can be also the "only" partition at the same time
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' SET INTERVAL( '||aPart.INTERVAL||' )';
DBMS_OUTPUT.PUT_LINE('Cannot drop the only partittion '||aPart.PARTITION_NAME ||' from table '||aPart.TABLE_NAME);
EXECUTE IMMEDIATE 'ALTER TABLE '||aPart.TABLE_NAME||' TRUNCATE PARTITION '||aPart.PARTITION_NAME|| ' UPDATE GLOBAL INDEXES';
DBMS_OUTPUT.PUT_LINE('Truncated partittion '||aPart.PARTITION_NAME ||' from table '||aPart.TABLE_NAME);
END;
END;
END IF;
END LOOP;
END;