Re: count(*) ?

"shakespeare" <whatsin_at_xs4all.nl> schreef in bericht news:478dc155$0$85778$e4fe514c_at_news.xs4all.nl...
>
> "Frank van Bortel" <frank.van.bortel_at_gmail.com> schreef in bericht
> news:7767f$478cff47$524b5c40$12171_at_cache5.tilbu1.nb.home.nl...
>> nick wrote:
>>> I understand that when you feed the count( ) function an asterisk as
>>> an argument it runs
>>> slower than if you use a column name as an argument. Can someone tell
>>> me why this is so?
>>>
>>> Thanks
>> Test it - it is not so - who do you believe?!?
>>
>> --
>>
>> Regards,
>> Frank van Bortel
>>
>> Top-posting in UseNet newsgroups is one way to shut me up
>
> O yes it is! If you have a sparse column (say col_a), indexed in a very
> large table, count(col_a) will use the index , where count(*) doesn't (and
> they will return different values as well).
> I think you confused this with select (*) and select (1) (which perform
> the same, although you might find a DBA at your current working place who
> is convinced that count (8) is faster.....). They ARE not the same though,
> for count(*) from table in a view will not invalidate a view when a column
> is added to the table, where count(1) will.....
>
> Shakespeare
>

mmm I must correct that, both views become invalid. Have seen examples of the contrary, will look them up and report....

Shakespeare Received on Wed Jan 16 2008 - 02:37:58 CST