Marks the start of a control loop. A LOOP statement enables you
    to execute the associated sequence of SQL statements called a
    compound statement. After SQL executes the statements within the
    loop, control returns to the LOOP statement at the top of the
    loop for subsequent statement execution. Looping occurs until
    SQL encounters an error exception or executes a LEAVE statement.
    In either case, SQL passes control out of the LOOP block to the
    statement immediately after the LOOP statement.