What is the difference between clustered and non-clustered indexes conceptually?

< 1 min read

Conceptually, a clustered index defines the physical order of data in a table.
It means the table rows are stored based on that indexed column.
In one project, the transaction table was clustered on Order Date to improve time-based queries.
A table can have only one clustered index because data can be sorted physically only one way.
A non-clustered index is a separate structure that stores key values with row references.
It does not change the physical order of the table.
We used non-clustered indexes on Customer ID and Product ID for frequent lookups.
So clustered affects storage order, while non-clustered acts like a lookup reference.

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