No, nothing will ever equal null. In strict relational theory, which I don't know well enough to begin expounding on here, null does not even equal another null. That's why SQL provides IS NULL and IS NOT NULL as explicit cases.
- michael dykman On Mon, Dec 28, 2009 at 2:32 PM, D. Dante Lorenso <da...@lorenso.com> wrote: > > Will anything ever be equal to NULL in a SELECT query? > > SELECT * > FROM sometable > WHERE somecolumn = NULL; > > I have a real-life query like this: > > SELECT * > FROM sometable > WHERE somecolumn = NULL OR somecolumn = 'abc'; > > The 'sometable' contains about 40 million records and in this query, it > appears that the where clause is doing a sequential scan of the table to > find a condition where 'somecolumn' = NULL. Shouldn't the query parser be > smart enough to rewrite the above query like this: > > SELECT * > FROM sometable > WHERE FALSE OR somecolumn = 'abc'; > > And therefor use the index I have on 'somecolumn'? When I manually rewrite > the query, I get the performance I expect but when I leave it as it was, > it's 100 times slower. > > What's so special about NULL? > > -- Dante > > ---------- > D. Dante Lorenso > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/mysql?unsub=mdyk...@gmail.com > > -- - michael dykman - mdyk...@gmail.com "May you live every day of your life." Jonathan Swift Larry's First Law of Language Redesign: Everyone wants the colon. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
