Identify the missing word(s) in the following sentence within the context of Microsoft Azure. SQL Server has several index types to support different types of workloads. At a high level, an index can be thought of as an on-disk structure that is associated with a table or a view, that enables SQL Server to more easily find the row or rows associated with the index key, compared to scanning the entire table. [?] are a separate structure from the data rows. [?] contain the key values defined for the index, and a pointer to the data row that contains the key value. You can add additional nonkey columns to the leaf level of [?] to cover more columns using the included columns feature in SQL Server. You can create multiple [?] on a table.