How to make Oracle ALTER TABLE MODIFY script be idempotent?

Question

I have this migration script;

ALTER TABLE table_name MODIFY (column_name NULL);

How do I make it idempotent?

Answer 1

Either you can use an exception handler:

DECLARE
    CANNOT_MODIFIY_TO_NULL EXCEPTION;
    PRAGMA EXCEPTION_INIT(CANNOT_MODIFIY_TO_NULL, -1451);
BEGIN

    EXECUTE IMMEDIATE 'ALTER TABLE TABLE_NAME MODIFY (column_name  NULL)';
exception
    when CANNOT_MODIFIY_TO_NULL then
        NULL;
END;

or check NULLABLE in view USER_TAB_COLUMNS:

DECLARE

    CURSOR Cols IS
    SELECT COLUMN_NAME 
    FROM USER_TAB_COLUMNS 
    WHERE TABLE_NAME = 'TABLE_NAME' 
        AND NULLABLE = 'N' 
        AND COLUMN_NAME = 'COLUMN_NAME';

BEGIN
    FOR aCol IN Cols LOOP
        EXECUTE IMMEDIATE 'ALTER TABLE TABLE_NAME MODIFY ('||aCol.COLUMN_NAME||' NULL)';
    END LOOP;
END;