Database.Middle.What are the differences between clustered and non-clustered indexes?

Feature	Description
Data Storage	Physically reorders the table’s rows to match the index. The index is the table.
Only One	A table can have only one clustered index because data rows can be sorted in only one order.
Faster for Range Queries	Ideal for queries that return a range of values (e.g. `BETWEEN`, `ORDER BY`, `GROUP BY`) because data is stored in order.
Primary Key by Default	In many databases, the primary key automatically becomes the clustered index (unless specified otherwise).
Example Use	Indexing `customer_id` in a `Customers` table for fast lookup and sorting by ID.

Feature	Description
Separate from Data	Stores a copy of indexed columns and a pointer to the actual data row. The data remains in the original order.
Multiple Allowed	A table can have many non-clustered indexes (limited by DBMS).
Slower for Range Queries	Less efficient for large range scans due to extra lookup steps (called bookmark lookups or key lookups).
Flexible	Can be created on any column(s), useful for filtering or joining on non-primary fields.
Example Use	Indexing the `email` column in a `Users` table to speed up login queries.

Clustered index: Like a sorted dictionary, where entries are arranged by the word itself.
Non-clustered index: Like the index at the back of a textbook, pointing you to page numbers (locations of data).

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