Home Forums SQL Server 2008 T-SQL (SS2K8) t-sql key on a table RE: t-sql key on a table

  • January 6, 2014 at 10:09 pm

    #1677948

    Christian Graus (1/6/2014)

    I did not know that a clustered index is the default for a PK. Doesn't a clustered index mean the entire row is written in the index ?

    To be semantically correct, it means that the rows of the table form the leaf level of the Clustered Index and a B-Tree is built over the top of it. That's why a Clustered Index Scan is actually the same as a Table Scan except that a Table Scan can only happen on HEAPs because there is no Clustered Index on those.

    And, yeah... if you assign a Primary Key without explicitly assigning it as a Non-Clustered index and no Clustered Index has yet been assigned, the PK will be created as a UNIQUE Clustered Index along with the special PK meaning of "NOT NULL".

    --Jeff Moden

    RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
    First step towards the paradigm shift of writing Set Based code:
    ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

    Change is inevitable... Change for the better is not.

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