First - thank you. I want to again thank this list, which in general is the most tolerant to people new to database use and theory in general, and me in particular. I mostly got your point from an earlier answer. Hopeful your example quashes my ignorance, relative to NULL at least.
I think I understand the manual examples with the help of the answers I got. I was not getting it on my own. On Tue, 20 Sep 2005, Joerg Bruehe wrote: > Hi! > > > Just some explicit addition: > > [EMAIL PROTECTED] wrote: > > [[...]] > > > > So in the following query: > > > > select * from new_payments where closed<>1; > > > > it is desired that null=1. DeMorgan's law takes a vacation here. > > You use two-valued logic here, where statements are either "true" or > "false". (DeMorgan's law applies to two-valued logic only.) > > When NULL values are not excluded, SQL uses a three-valued logic, where > a stament may also be "unknown". Comparing NULL to any value (including > a comparison of NULL and NULL) always results in "unknown". > > This also the reason that the SQL syntax does not allow > ... WHERE value = NULL > but requires that you write > ... WHERE value IS NULL > It has also been said that NULL is no value but a state - maybe that > helps in understanding. > > > HTH, > Jörg > > -- > Joerg Bruehe, Senior Production Engineer > MySQL AB, www.mysql.com > _____ Douglas Denault http://www.safeport.com [EMAIL PROTECTED] Voice: 301-469-8766 Fax: 301-469-0601 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
