This illustration is a tree depicting the execution plan for the statement in the preceding text. Step 1, View emp_group_by_deptno, is a clear box that branches to Step 2, Sort (group by), a clear box. Step 2 branches to Step 3, Table Access (by rowid) emp, a shaded box. Step 3 branches to Step 4, Index (range scan) emp_deptno_index, a shaded box. For an explanation of the meaning of clear and shaded boxes, see the "Steps in the Execution Plan" section in Chapter 1.