Re: Joins with nulls
Date: Thu, 21 Nov 2002 18:33:03 GMT
Add to what you said, that nulls are themselves the result of outer joins on the underlying data.
A relational model of the data will not have any nulls in it. Optional columns in tabulated data, (SQL style data) are a consequence of denormalizing the relational model, although it often doesn't look that way to non theoretical types like myself.
Take a column like "Middle Initial" in a table that's describing persons. If you really want to avoid NULLS, and you don't want to cheat, you need a table that contains two attributes (Person_ID, Middle_Initial). Now all you have to do is to leave out the row for people who don't have a middle initial. Presto! There aren't any NULLS.
However, I DON'T recommend this as a practical solution in, say, a payroll system. I recommend an optional column, as disgusting as this may seem to the theorists. Received on Thu Nov 21 2002 - 19:33:03 CET