How to change (decrease) primary key column length?

Question

Hi all,
I have plenty of data in the table and I need to decrease the primary key column from CHAR(17) to CHAR(13).
I try to use:
ALTER TABLE xx MODIFY (prmy_key (13));
but Oracle give:
ERROR at line 1:
ORA-01441: column to be modified must be empty to decrease column length
Can anyone give me advice on what is the best way to decrease column length? Thanks in advance for your help.

Answer 1

To add to the above, I have done a simple test in the lines that I was suggesting the solution for this problem,
   CREATE TABLE testA
   (pk_col   varchar2(20), jd date, constraint pk1 PRIMARY KEY(pk_col));
   --Insert data into testA
   create table testB as select * from testA;
   TRUNCATE table testA;
   ALTER TABLE testA modify(pk_col VARCHAR2(10));   
   INSERT INTO testA SELECT substr(pk_col, 1, 10), jd from testB;
   DROP TABLE testB;
   Select constraint_name, constraint_type, status from all_constraints
   Where table_name = 'TESTA';
   CONSTRAINT_NAME                C STATUS
   PK1                            P ENABLEDAlter command is successful as the table is empty. TRUNCATE flushes the data and resets the high water mark keeping all the constraints. If we safely want to use the TRUNCATE as far as storage issues are concerned,
TRUNCATE table table_name reuse storage;
I think, this would accoplish what has been asked.
Let me know,
SriDHAR