How to work around ORA-38323: policy conflicts with policy

You try to enable a tablespace-wide ADO policy:

ORA-38323: policy conflicts with policy 42

If you lookup the error with oerr ora 38323, oracle will give you the following solution:

* Cause: An attempt was made to create a policy with the same action
         type and based on the same statistic as another policy on the
         object.
 *Action: Use a different action and/or statistic for the new policy,
          or delete the old policy.

Verify that there is a policy on the tablespace already:

SELECT * 
FROM DBA_ILMPOLICIES 
WHERE TABLESPACE IS NOT NULL;

Result:

POLICY_NAME	POLICY_TYPE	TABLESPACE	ENABLED	DELETED
P43	DATA MOVEMENT	DATA1	YES	NO

Theres is indeed a policy named P43. What kind of policy is it?

SELECT policy_name,action_type,scope,compression_level,condition_type,condition_days,policy_subtype
FROM DBA_ILMDATAMOVEMENTPOLICIES 
WHERE POLICY_NAME IN (SELECT POLICY_NAME FROM DBA_ILMPOLICIES WHERE TABLESPACE IS NOT NULL); 

Result:

POLICY_NAME	ACTION_TYPE	SCOPE	COMPRESSION_LEVEL	CONDITION_TYPE	CONDITION_DAYS	POLICY_SUBTYPE
P43	COMPRESSION	GROUP	ADVANCED	LAST ACCESS TIME	1	DISK

So the policy is a directive to the oracle server to compress all objects after one day of no access. If you need to alter this policy, the old one must be dropped:

ALTER TABLESPACE DATA1 DEFAULT ILM DELETE POLICY P43;

You are now free to add a new ADO policy to the tablespace:

ALTER TABLESPACE DATA1
DEFAULT ILM ADD POLICY
ROW STORE COMPRESS ADVANCED
GROUP AFTER 30 DAYS OF NO ACCESS;