PROBLEM:

Got error while doing online redefinition of a table, ORA-01442: column to be modified to NOT NULL is already NOT NULL.

DECLARE
   error_count pls_integer := 0;
BEGIN
    DBMS_REDEFINITION.COPY_TABLE_DEPENDENTS('RAJDBA', 'SOC_TABLE', 'SOC_TABLE_INTERIM', dbms_redefinition.cons_orig_params, TRUE,TRUE,TRUE,FALSE, error_count);
    DBMS_OUTPUT.PUT_LINE('errors := ' || TO_CHAR(error_count));
END;
/
Session altered.

SQL>
Session altered.

SQL> SQL> SQL>   2    3    4    5    6    7
DECLARE
*
ERROR at line 1:
ORA-01442: column to be modified to NOT NULL is already NOT NULL
ORA-06512: at "SYS.DBMS_REDEFINITION", line 1746
ORA-06512: at "SYS.DBMS_REDEFINITION", line 2626
ORA-06512: at "SYS.DBMS_REDEFINITION", line 4009
ORA-06512: at line 4

SOLUTION:

Check whether you have any not null constraint present on the interim table:

SQL>  select owner,CONSTRAINT_NAME,CONSTRAINT_TYPE,search_condition from dba_constraints where owner='RAJDBA' and table_name='SOC_TABLE_INTERIM' ;

-- if any not null constraint is reported, drop them.

SQL> alter table  "RAJDBA"."SOC_TABLE_INTERIM" drop constraint SYS_C0013751;

Table altered.

SQL> alter table  "RAJDBA"."SOC_TABLE_INTERIM" drop constraint SYS_C0013752;

Table altered.

SQL>  alter table  "RAJDBA"."SOC_TABLE_INTERIM" drop constraint SYS_C0013750;

Table altered.

Now rerun the DBMS_REDEFINITION.COPY_TABLE_DEPENDENTS process, it should work fine.

DECLARE
   error_count pls_integer := 0;
BEGIN
    DBMS_REDEFINITION.COPY_TABLE_DEPENDENTS('WMBREL', 'STC_BREL_AUDIT', 'STC_BREL_AUDIT_INT', dbms_redefinition.cons_orig_params, TRUE,TRUE,TRUE,FALSE, error_count);
    DBMS_OUTPUT.PUT_LINE('errors := ' || TO_CHAR(error_count));
END;
/


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PL/SQL procedure successfully completed