This illustration is a tree depicting the execution plan for the statement in the preceding text. Step 1, Filter, is a clear box that branches to Step 2, Nested Loops, a clear box, and Step 6, Table Access (full) salgrade, a shaded box. Step 2 branches to Step 3, Table Access (full) emp, and Step 4, Table Access (by rowid) dept, which are both shaded boxes. Step 4 branches to Step 5, Index (unique scan) pk_deptno, 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.