Starts a transaction and specifies its characteristics. A
    transaction is a group of statements whose changes can be made
    permanent or undone only as a unit.

    A transaction ends with a COMMIT or ROLLBACK statement. If you
    end the transaction with the COMMIT statement, all the changes
    made to the database by the statements are made permanent. If you
    end the transaction with the ROLLBACK statement, the statements
    do not take effect.

    You must end the transaction with a COMMIT or ROLLBACK statement
    before starting or declaring another transaction. If you try to
    start or declare a transaction while another one is active, SQL
    generates an error message.

    Besides the SET TRANSACTION statement, you can specify the
    characteristics of a transaction in one of two other ways:

    o  If you specify the DECLARE TRANSACTION statement, the
       declarations in the statement take effect when SQL starts a
       new transaction that is not started by the SET TRANSACTION
       statement. SQL starts a new transaction with the first
       executable data manipulation or data definition statement
       following the DECLARE TRANSACTION, COMMIT, or ROLLBACK
       statement.

    o  If you omit both the DECLARE and SET TRANSACTION statements,
       SQL automatically starts a transaction (using the read/write
       option) with the first executable data manipulation or data
       definition statement following a COMMIT or ROLLBACK statement.
       Thus, you can retrieve and update data without declaring or
       setting a transaction explicitly.

    See the Oracle Rdb SQL Reference Manual for examples of when you
    would want to use the DECLARE TRANSACTION statement instead of
    the SET TRANSACTION statement.

    You can specify many options with the SET TRANSACTION statement,
    including:

    o  Transaction mode (READ ONLY/READ WRITE)

    o  Lock specification clause (RESERVING options)

    o  Horizontal partition specification (RESERVING options)

    o  Wait mode (WAIT/NOWAIT)

    o  Isolation level

    o  Constraint evaluation specification clause

    o  Multiple sets of all the preceding options for each database
       involved in the transaction (ON . . . AND ON)

    The Arguments section explains these options in more detail.