SQL> drop table t cascade constraints purge;

Table dropped.

SQL> create table t ( x int, y date )
  2  partition by range ( y )
  3  interval ( numtodsinterval(1,'DAY'))
  4  (
  5  partition p1 values less than ( date '2016-01-01' )
  6  );

Table created.

SQL>
SQL> insert into t
  2  select rownum, date '2015-12-31' + rownum / 1000
  3  from dual
  4  connect by level <= 1000 * 40;

40000 rows created.

SQL>
SQL> commit;

Commit complete.

SQL>
SQL> exec dbms_stats.gather_table_stats('','T');

PL/SQL procedure successfully completed.

SQL>
SQL> exec dbms_stats.lock_table_stats('','T');

PL/SQL procedure successfully completed.

SQL>
SQL> select table_name, num_rows from user_tables where table_name = 'T';

TABLE_NAME                       NUM_ROWS
------------------------------ ----------
T                                   40000

1 row selected.

SQL> select partition_name, num_rows from user_tab_partitions where table_name = 'T';

PARTITION_NAME         NUM_ROWS
-------------------- ----------
P1                          999
SYS_P14304                 1000
SYS_P14305                 1000
SYS_P14306                 1000
SYS_P14307                 1000
SYS_P14308                 1000
SYS_P14309                 1000
SYS_P14310                 1000
SYS_P14311                 1000
SYS_P14312                 1000
SYS_P14313                 1000
SYS_P14314                 1000
SYS_P14315                 1000
SYS_P14316                 1000
SYS_P14317                 1000
SYS_P14318                 1000
SYS_P14319                 1000
SYS_P14320                 1000
SYS_P14321                 1000
SYS_P14322                 1000
SYS_P14323                 1000
SYS_P14324                 1000
SYS_P14325                 1000
SYS_P14326                 1000
SYS_P14327                 1000
SYS_P14328                 1000
SYS_P14329                 1000
SYS_P14330                 1000
SYS_P14331                 1000
SYS_P14332                 1000
SYS_P14333                 1000
SYS_P14334                 1000
SYS_P14335                 1000
SYS_P14336                 1000
SYS_P14337                 1000
SYS_P14338                 1000
SYS_P14339                 1000
SYS_P14340                 1000
SYS_P14341                 1000
SYS_P14342                 1000
SYS_P14343                    1

41 rows selected.

SQL>
SQL> alter table t set interval () ;

Table altered.

SQL>
SQL> declare
  2    tot_rows int;
  3    tot_blks int;
  4
  5    par_rows int;
  6    par_blks int;
  7
  8    par_name varchar2(30);
  9  begin
 10    select num_rows, partition_name , blocks
 11    into par_rows, par_name, par_blks
 12    from user_tab_partitions
 13    where table_name = 'T'
 14    and   partition_position = 1;
 15
 16    select num_rows , blocks into tot_rows, tot_blks
 17    from user_tables
 18    where table_name = 'T';
 19
 20    execute immediate 'alter table t drop partition '||par_name;
 21
 22    dbms_stats.set_table_stats(
 23      '','T',
 24      numrows=> tot_rows - par_rows,   -- adjust total rows downwards because we dropped a partition
 25      numblks=>tot_blks - par_blks,    -- adjust total blocks downwards because we dropped a partition
 26      force=>true );  -- override the lock
 27  end;
 28  /

PL/SQL procedure successfully completed.

SQL>
SQL>