The table in Figure 9-7 shows a nonclustered index on lname. The data rows at the far right show pages in ascending order by employee_id (10, 11, 12, and so on) because there is a clustered index on that column.
The root and intermediate pages store:
The key value
The row ID
The pointer to the next level of the index
The leaf level stores:
The key value
The row ID
The row ID in higher levels of the index is used for indexes that allow duplicate keys. If a data modification changes the index key or deletes a row, the row ID positively identifies all occurrences of the key at all index levels.
Figure 9-7: Nonclustered index structure
