Q: Please explain the concepts of transaction, commit and rollback

A sequence of database modifications, i.e., a sequence of insert, update, and delete statements,is called a transaction.
These modifications are temporarily stored in the database system. They become permanent only after the statement commit; has been issued.
As long as the user has not issued the commit statement, it is possible to undo all modifications since the last commit. To undo modifications, one has to issue the statement rollback;.
All statements between two commits or a commit and a rollback form one transaction. Please note that all ddl statements are autocommit.