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I was wondering how are null values stored on DISK - is it allocating some minimum bytes - physical disk space as for other columns which have indeed some values and arranged contiguously as the rows are inserted into a table?

and a second question is: if the null values are updated with values, SQL will assign the space needed available at the end of the data file ?


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up vote 4 down vote accepted

Each row has a null bitmap for columns that allow nulls. If the row in that column is null then a bit in the bitmap is 1 else it's 0.

Pardon me for linking to the cached version of the article from which that is taken.

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