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Message Posted: Wed, 06 Jun 2007 @ 18:12:22 GMT

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Subj:   Re: Null Value
From:   DWellman


Yes it does depend on the type of field and also whether or not the column is compressed.

Each NULLable column requires one "presence bit" which is stored in the row header.

If a column contains NULL and is compressed (remember that if you specify compression on any value in Teradata the NULLs are also compressed) then the only physical space required is for the presence bit.

- if you've got compression involved remember that there are also presence bits required for compression.

If a column contains NULL and is NOT compressed, then the phsyical space required is the space that would normally be used by a non-NULL value - e.g. a DATE column will require 4 bytes, a CHAR(10) will require 10 bytes. If the column is a VARCHAR and contains NULL then (I think) it requires 0 bytes, but it may be 2 bytes for the variable length indicator, I'm not sure.



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