What is key and non-key column wrt to indexes

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What is key and non-key column wrt to indexes

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Shadab Shah

Posted Tuesday, December 11, 2012 4:24 AM

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Hi,
Since this might be the most basic question hence i did not find its answer anywhere. Could anybody tell me what is mean by Key & Non-Key column with respect to indexes.

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anthony.green

Posted Tuesday, December 11, 2012 4:27 AM

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A key column is the column(s) that the index is created on, the non-key column are included columns

CREATE NONCLUSTERED INDEX idx1 ON Table1 (Col1, Col2) INCLUDE (Col3, Col4)

In the above example, Col1 and Col2 are key columns, Col3 and Col4 are non-key columns

CREATE CLUSTERED INDEX cidx ON Table1 (Col1)

In the above example Col1 is the key column, and all other columns in the table are classed as non-key columns, as the clustered index is the table.

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