Test insert update success

HI,

I have many question to post because I returned to Cobol years later. The most important question regards the database pre-compiler. In particular:

1) With EXEC SQL Can I set isolation level and begin transaction ?

2) How Can I test if an insert or updated does not succeed because of constraints violations?

3) If I set autocommit disabled in SQl properties can I use commit and rollback ?

4) To set a null value it is sufficient move -1 to :name-fileld-null  ?

Claudio