hi,

Could you please tell me whether null values consume space in db2 .I am on db2V9.5 on aix ...

consumes space? NULL values?

don't confuse null with vacuum.

and 'null values' is an improper use of the terms.
null indicates that there is no value (data) associated with this column in this row.

In fact, a nullable column carries within the file structure supporting db2 an additional
field to indicate if the column is null or not null.

null or not null tells db2 whether to return a value for a column.

so actually, a nullable column whether null or not null, consumes more space that a 'not null column'.

Aside from the fact that NULL is not a value (because it is an inherent property that you can compare one value with another value of the same domain, which you can't do with NULLs), each nullable value requires an additional byte to be stored, i.e. the null indicator. So the answer is "yes", it consumes space.

Hopefully I am not being redundant, but:

If a column is defined in the create table as NOT NULL, it always takes up one less byte of storage compared to a column that is nullable. This is true regardless of whether a particular row has a null value or not null value for that column.

Along similar lines, a VARCHAR column requires 2 extra bytes of storage to store the length of the actual value being stored on any given row for that column value. This is true whether the value is null or not null.

So a VARCHAR column that is nullable always takes up 3 extra bytes compared to a CHAR column defined as NOT NULL (although obviously a VARCHAR column may require less storage than CHAR for the actual data if the entire length is not used).