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Message Posted: Mon, 16 Jan 2012 @ 13:48:29 GMT

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Subj:   Re: Compress Null value
From:   Machha Narayan Rao Naidu


You will not get any significant changes in terms of Disk space while compressing NULL. If the no. of NULL's are large then you can see a little changes probably.

Below is the chart From Teradata manual on % Compression.

The following table shows example compressibility for fields of 1 and 4 bytes. "Percent compression" is the savings when considering the compressed size in comparison to the uncompressed size.

                    Frequency of
     Field Width    Single Value      Percent
     (Bytes)        (and NULL)        Compression
        1               20%              7%
        1               50%             37%
        1               80%             67%
        4               20%             17%
        4               50%             47%
        4               80%             77%

Note that the compression savings are for a particular column. Overall system savings is dependent on the number of columns that are compressed and the individual savings from each column.



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