Question

I have the following transaction:

1. SQL inserts a 1 new record into a table called tbl_document
2. SQL deletes all records matching a criteria in another table called tbl_attachment
3. SQL inserts multiple records into the tbl_attachment

Until this transaction finishes, I don’t want others users to be aware of the (1) new records in tbl_document, (2) deleted records in tbl_attachment, and (3) modified records in tbl_attachment.

Would Read Committed Isolation be the correct isolation level?

Answer 1

yes, like this:

BEGIN TRANSACTION

   insert into tbl_document ...
   delete tbl_attachment where ...
   inserts into tbl_attachment ...

COMMIT

you may block/lock users until you are finished and commit/rollback the transaction. Also, someone could SELECT your rows from tbl_attachment after your insert into tbl_document but before your delete. If you need to prevent that do this:

BEGIN TRANSACTION

   select tbl_attachment with (UPDLOCK,HOLDLOCK) where ...
   insert into tbl_document ...
   delete tbl_attachment where ...
   inserts into tbl_attachment ...

COMMIT

or just delete tbl_attachment before the insert into tbl_document and forget the select with the locking hints.