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? http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html Should answer some of your questions, Dante.
