Rule-based and Cost-based.
select to_number(rollnumber) from tname order by rollnumber
Commit, Rollback, DCL command like grant revoke.When exit from oracle (implicite commit happened), When database abnormally closed then an implicit rollback happened. When user invokes an DDl command
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.
Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.