DBMS: Non-Clustered Index (Definitions)

"An index that stores key values and pointers to data. The leaf level points to data pages rather than containing the data itself." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"A nonclustered index does not physically arrange data, but points to the data in a table. The pointers are themselves sorted, making it easy to quickly locate data (search) within a table." (Owen Williams, "MCSE TestPrep: SQL Server 6.5 Design and Implementation", 1998)

"An index with a structure completely separate from the data rows it indexes; normally a B-tree. The lowest rows of a non-clustered index contain the index key values, with each key value pointing to the data rows that contain that key. The data rows are not stored in an order based on the index key, but rather in a heap." (Peter Gulutzan & Trudy Pelzer, "SQL Performance Tuning", 2002)

"An index in which the logical order of the index is different than the physical, stored order of the rows on disk." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"An index in which the logical order of the index is different than the physical, stored order of the rows on disk. In contrast to clustered indexes, non-clustered indexes are totally separated from the actual data rows, causing an unsorted order of data based on non-clustered keys. Non-clustered indexes differ from the clustered indexes at the leaf level. The leaf level of a non-clustered index contains the key value and the row locator. The row locator is either the physical row address (if there is no clustered index) or the clustered index key value (if a clustered index exists)." (Thomas Moore, "EXAM CRAM™ 2: Designing and Implementing Databases with SQL Server 2000 Enterprise Edition", 2005)

"This is an index that does not physically rearrange the data that is inserted into your tables. This index contains pointers to the data that is stored in the table or clustered index." (Joseph L Jorden & Dandy Weyn, "MCTS Microsoft SQL Server 2005: Implementation and Maintenance Study Guide - Exam 70-431", 2006)

"An index in which the logical order of the index is different from the physical, stored order of the rows on disk. In contrast to clustered indexes, non-clustered indexes are totally separated from the actual data rows, causing an unsorted order of data based on non-clustered keys. Non-clustered indexes differ from clustered indexes at the leaf level. The leaf level of a non-clustered index contains the key value and the row locator. The row locator is either the physical row address (if there is no clustered index) or the clustered index key value (if a clustered index exists)." (Thomas Moore, "MCTS 70-431: Implementing and Maintaining Microsoft SQL Server 2005", 2006)

"A SQL Server index that is separate from the table." (Marilyn Miller-White et al, "MCITP Administrator: Microsoft® SQL Server™ 2005 Optimization and Maintenance 70-444", 2007)

"An index whose leaf level stores only the columns included in the index (key columns and included columns) and holds pointers to the rows in the actual table." (Sara Morganand & Tobias Thernstrom , "MCITP Self-Paced Training Kit : Designing and Optimizing Data Access by Using Microsoft SQL Server 2005 - Exam 70-442", 2007)

"A non-clustered index is added to optimize queries. Tables can have multiple non-clustered indexes. A non-clustered index is similar to the index in the back of a book. By finding it in the index, you know specifically where to look in the book for the information." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

"A non-clustered index is an index that stores the clustering key or row ID to the row data in its leaf nodes, depending on whether the table is a clustered table or a heap." (Michael Coles, "Pro T-SQL 2008 Programmer's Guide", 2008)

"An index in which the logical order of the index key values is different than the physical order of the corresponding rows in a table. The index contains row locators that point to the storage location of the table data." (Microsoft, "SQL Server 2012 Glossary", 2012)

"A non-clustered index is an index that stores the clustering key or row ID to the row data in its leaf nodes, depending on whether the table is a clustered table or a heap." (Jay Natarajan et al, "Pro T-SQL 2012 Programmer's Guide" 3rd Ed., 2012)

"An index that stores the clustering key or row ID of the row data in its leaf nodes, depending on whether the table is a clustered table or a heap." (Miguel Cebollero et al, "Pro T-SQL Programmer’s Guide" 4th Ed., 2015)