A nonclustered index is a separate database object that provides another ordering or lookup path to table rows. Unlike a clustered index, it does not determine the table’s physical order, so one table can have several nonclustered indexes. section 19.3.2 section 19.3
Think of a library catalog: search by a book’s title, find its numeric location, then go to the shelf. A nonclustered index similarly finds matching values and points toward the table rows, avoiding an unnecessary scan of the entire table. section 19.3.2
Speeding a shipment-date report
A report counting shipments for one date can use an index on ShipmentDate: CREATE INDEX IX_shipment_ShipmentDate ON shipment (ShipmentDate); The index helps locate the relevant date instead of reading the entire shipment table. Keep indexes focused: extra columns consume storage and add work to INSERT, UPDATE, and DELETE operations. section 19.5 section 19.3.2
CREATE INDEX IX_shipment_TrackingNumber ON shipment (TrackingNumber);
Inspect a complete CREATE INDEX statement for a shipment tracking number. section 19.3.2
