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