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RE: What's the count?

Paul White — Wed, 31 Mar 2010 09:34:03 GMT

[quote][b]timothy.g.parker (3/31/2010)[/b][hr]It should be noted, that depending on your record sets, the count(*) should be replaced with count_big(*) to give the you the correct results.[/quote]Ever wonder why there's no SUM_BIG?

RE: What's the count?

timothy.g.parker — Wed, 31 Mar 2010 09:27:12 GMT

I tried the following statement on some existing tables[b]select count(*) from table1, table2[/b]to verify the results of the question. As it turns out, with my data set, the query returns the "Arithmetic overflow error converting expression to data type int". It should be noted, that depending on your record sets, the count(*) should be replaced with count_big(*) to give the you the correct results.

RE: What's the count?

Paul White — Tue, 30 Mar 2010 08:12:08 GMT

Amazing that so many people are unaware of the syntax. Especially since it pre-dates the CROSS JOIN form.

RE: What's the count?

Peter Trast — Mon, 15 Mar 2010 11:19:27 GMT

Well, I guessed that it would cross join and got lucky :)Now I have a new way to do cross joins! Can't wait to kill my server with that one...

RE: What's the count?

Scott Arendt — Fri, 12 Mar 2010 06:45:31 GMT

Well I learned something today. I had no idea you could produce a cross join in that manner.

RE: What's the count?

sameerchachad 69959 — Fri, 12 Mar 2010 01:27:13 GMT

Good question. This was really a mind teaser. Never thought of doing a COUNT for two tables.

RE: What's the count?

Steve Cullen — Thu, 11 Mar 2010 13:55:07 GMT

My definition of a good QOD: Anytime I get the correct answer :-DGood Question!

RE: What's the count?

Oleg Netchaev — Thu, 11 Mar 2010 10:47:05 GMT

[quote][b]Carlo Romagnano (3/11/2010)[/b][hr]if one table has one o more rows and the other is void, the result is 0.NumberOfRows * 0 = 0[/quote]This is a very good feature of the count function, to still return 0 if there is nothing to count. This makes it different from other aggregates, which will return null if there is nothing to consider. For example,[code="sql"]use AdventureWorks;godeclare @one_or_more table ( DepartmentID smallint, [Name] nvarchar(50));declare @void table (DepartmentID smallint, [Name] nvarchar(50));-- insert 10 records into @one_or_more and leave @void emptyinsert into @one_or_more select top 10 DepartmentID, [Name] from HumanResources.Department;select count(*) RecordCount, min(A.DepartmentID) DepartmentID from @one_or_more A, @void B;go[/code]resulting in[code="plain"]RecordCount DepartmentID----------- ------------0 NULL[/code]illustrates the point. The cartesian product does not return anything because the @void has no records, the min(A.DepartmentID) is therefore null though the value of the first department in the @one_or_more is actually 1, but the count shines here as it still returns 0, not null. I am not saying that implementation of the count is better, but I find this feature extremely useful.This is a very good question, really liked it.Oleg

RE: What's the count?

sknox — Thu, 11 Mar 2010 09:01:18 GMT

[quote][b]wall str33t (3/11/2010)[/b][hr]A better question might be is there a difference between count(*) and count(col).Many people don't know the subtleties between them.[/quote]Rather than re-answer that question, I'll provide a link to where you can find that information:[url]http://www.sqlservercentral.com/Forums/FindPost879366.aspx[/url] -- My post explaining how COUNT_BIG works[url]http://www.sqlservercentral.com/Forums/FindPost879538.aspx[/url] -- Oleg's excellent test setup illustrating my explanation These are from the discussion of the March 9 QotD by agrawal.prakriti, about COUNT_BIG. The only difference between COUNT_BIG and COUNT is that COUNT_BIG returns a BIGINT rather than an INT. For official reference:[url]http://msdn.microsoft.com/en-us/library/ms190317.aspx[/url] -- Microsoft's documentation for COUNT_BIG[url]http://msdn.microsoft.com/en-us/library/ms175997.aspx[/url] -- Microsoft's documentation for COUNTFeel free to write and submit a QotD based on this info.

RE: What's the count?

wall str33t — Thu, 11 Mar 2010 08:40:03 GMT

A better question might be is there a difference between count(*) and count(col).Many people don't know the subtleties between them.

RE: What's the count?

cajun_sql — Thu, 11 Mar 2010 08:19:27 GMT

Nice one - thanks. I just "recovered" from a Cartesian Product, myself. :-)

RE: What's the count?

Daniel Bowlin — Thu, 11 Mar 2010 08:08:56 GMT

This one definitely made me think a minute or two.

RE: What's the count?

nigel. — Thu, 11 Mar 2010 03:43:16 GMT

Very good question.However I think that the explanation is a bit lacking, and could explain in more detail what is happening here and what a 'cross join'/'cartesian product' is.Here are some links that may help:[url=http://msdn.microsoft.com/en-us/library/ms190690.aspx][u]Cross Join[/u][/url][url=http://en.wikipedia.org/wiki/Cartesian_product][u]Cartesian Product[/u][/url]

RE: What's the count?

kaspencer — Thu, 11 Mar 2010 02:31:47 GMT

That's is a good question, illustrating the need for careful joins!For those that don't know, this kind of result is called a "cartesian product", and if you allow it to happen in a real-world application with even a few hundred rows in either table, you are in for something of an explosion of complaints from your users, to say the least.Ken.

RE: What's the count?

Sree Divya — Thu, 11 Mar 2010 02:03:52 GMT

In Point of Interview Very Intelligence Question ......Nice...hmmmmm My Answer is Correct............!

RE: What's the count?

Carlo Romagnano — Thu, 11 Mar 2010 01:05:42 GMT

if one table has one o more rows and the other is void, the result is 0.NumberOfRows * 0 = 0

RE: What's the count?

aamirjani4u — Thu, 11 Mar 2010 00:50:04 GMT

count is basically. Counting the each record of that table. For Example. Table A has 3 rows then count = 3. if table B has 4 Rows then count=4. If combine both tables then 3 * 4 = 12 rows and count = 12

RE: What's the count?

jshailendra — Thu, 11 Mar 2010 00:13:42 GMT

Good question..never thought of using count(*) for 2 tables in one T-SQL...thanks for question

RE: What's the count?

Sree Arjun Div — Wed, 10 Mar 2010 23:19:21 GMT

Nice Question ....Today i learned this from Central...Good Question

RE: What's the count?

SQLRNNR — Wed, 10 Mar 2010 23:02:03 GMT

Thanks for the question. Nice job.

What's the count?

Slick84 — Wed, 10 Mar 2010 21:18:38 GMT

Comments posted to this topic are about the item [B]What's the count?[/B]