SQL Server 2017 Administration Inside Out by William Assaf & Randolph West & Sven Aelterman & Mindy Curnutt

Author:William Assaf & Randolph West & Sven Aelterman & Mindy Curnutt [Assaf, William]
Language: eng
Format: epub
Publisher: Pearson Education
Published: 2018-02-26T00:00:00+00:00

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NOTE

This chapter does not include any coverage of indexes, though a primary key is always associated with an index. Frequently, foreign keys are also indexed as their values are often used to query the table. For information on indexing, see Chapter 9 and Chapter 10.

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A table can have exactly one primary key. The primary key can consist of multiple columns, in which case it’s referred to as a compound primary key. However, in no case can a nullable column be (part of) the primary key. If additional columns’ values should be unique, you can apply a unique index or constraint. (See the next section for coverage on constraints.)

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