'null' values

I am looking for information about (a) the internal representation of 'null' values and (b) the treatment of 'null' values, in the major commercial relational DBMSs. (a) How are 'null' values *internally* represented in the DBMS ? e.g. by means of some reserved value in the range of possible values, or by means of some invalid value, for each type of field supported by the DBMS; by means of some (hidden) extra bit/byte; .... (b) As to the treatment of 'null' values, does the DBMS deviate from the SQL2 standard in any way ? Many thanks in advance for your replies, Regards, Ria. ----------------------------------------------------------- Ria Vandenberghe Ria.Vandenberghe@rug.ac.be UNIVERSITY OF GHENT (BELGIUM) - Computer Science Laboratory Technologiepark-Zwijnaarde 9, B-9052 ZWIJNAARDE, BELGIUM tel: +32/9/264.55.10 fax: +32/9/264.58.42