SQL: Using NULL values vs. default values

Question

What are the pros and cons of using NULL values in SQL as opposed to default values?

Answer 1

Nulls NEVER save storage space in DB2 for OS/390 and z/OS. Every nullable column requires one additional byte of storage for the null indicator. So, a CHAR(10) column that is nullable will require 11 bytes of storage per row – 10 for the data and 1 for the null indicator. This is the case regardless of whether the column is set to null or not.

DB2 for Linux, Unix, and Windows has a compression option that allows columns set to null to save space. Using this option causes DB2 to eliminate the unused space from a row where columns are set to null. This option is not available on the mainframe, though.

REF: http://www.craigsmullins.com/bp7.htm

So, the best modeling practice for DB2 Z/OS is to use "NOT NULL WITH DEFAULT" as a standard for all columns. It's the same followed in some major shops I knew. Makes the life of programmers more easier not having to handle the Null Indicator and actually saves on storage by eliminating the need to use the extra byte for the NULL INDICATOR.