Primary Key vs Clustered Unique Index

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K. Brian Kelley SSC Guru Points: 114704 More actions · Answer 1

1) A primary key can be non-clustered.

2) A unique index will allow one null value. Of course, if the column is set to NOT NULL, it won't.

K. Brian Kelley

Author: Start to Finish Guide to SQL Server Performance Monitoring

K. Brian Kelley
@kbriankelley

Steve Jones - SSC Editor SSC Guru Points: 739542 More actions · Answer 2

Two different things. Logically. The PK is the unqiue identifier for the data row. A unique index preseves uniqueness in the column.

Physically they are implemented the same.

Steve Jones

VMiccio Mr or Mrs. 500 Points: 588 More actions · Answer 3

Thanks! Always looking for a better understanding of what's under the hood.