Re: count(*) ?
Date: Thu, 17 Jan 2008 11:42:42 +0100
"Frank van Bortel" <frank.van.bortel_at_gmail.com> schreef in bericht
> shakespeare wrote:
>> "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 >> >>
> No I was not confused, though have to admit I misread the
> column name bit.
> The title had the start of another count(1) (or count(42),
> for that matter) is better (or worse) that count(*).
> That myth I wanted to stop right here.
> As far as the count(col) vs count(*) myth:
> Of course, assuming you want to know how many
> entries your table has (so not hanky-panky with
> nullable columns!)
> Frank van Bortel
> Top-posting in UseNet newsgroups is one way to shut me up
Sorry, that's what I meant too, but I wrote "select" where I should have
And about hanky panky: it's nullable columns that make the difference in count(column) and count(*) (different speed, different results). The "myth" article is about count(1), count(*) and count (rowid) and things like that.
Shakespeare Received on Thu Jan 17 2008 - 04:42:42 CST