COUNT(*)
COUNT(1)
COUNT(Column)
COUNT(DISTINCT Column)

COUNT(DISTINCT Column) looks for distinct values in the column, so it has a bunch of extra work to do.
COUNT(Column) looks for non-null values in that column, so it still has to read through it, unless the column doesn’t allow null, in which case it really just has to think about how many rows there are.
So COUNT(1) sounds very similar to COUNT(Column) when Column doesn’t allow nulls – but SQL sees it’s a constant and handles it as such, just counting rows.
And COUNT(*) is a recognised pattern which is understood as “just count rows”.

So COUNT(1) and COUNT(*) should be regarded as the same. I prefer COUNT(*) as it’s considered a recognised pattern. I never both using COUNT(1) – especialy since if you’re doing something like SUM(CASE…END), then you might have values of 1, 0, -1, whatever, being produced by your CASE statement, and so when I see COUNT(1), I have to start wondering whether it’s actually what I want or not. Plus, the old “ORDER BY 1″ gives meaning to the 1, and I don’t want any kind of confusion around that either.

Hope this helps,

Rob

what is the different between COUNT(*) and COUNT(1) which is better regarding performance and optimization ?

Thank you,

Second example do not give error.
also count do not count null values.It shows 0 for it.
in your example,if values of @A is 0 or above then its count is 1.
See one more example,

declare @t table(a varchar(10))
insert into @t values (null)
insert into @t values (”)
insert into @t values (‘abc’)
Select COUNT(a) from @t –Output is 2 because count() do not count null values

If we write,
Select count(*) from @t–Output is 3,because here we are telling count() to provide number of rows.

I have one question :)
Please execute the following Queries…!

SELECT COUNT(NULL) — this will generate error

GO

DECLARE @A INT
SET @A=NULL
SELECT COUNT(@A) ––this will not generate error why??

i am new to sql server and was browsing for the solution.
found a link in msdn
http://social.msdn.microsoft.com/forums/en-US/transactsql/thread/feba220c-4b43-4401-9711-e55198cff39e/
so do you agree with those comments??

Select * will throw an error because * is a wild character and not a function and function returns a value.

plz anybody reply me,

i got an error of 14262 in log shipping configuration

actually what i done is iam just started using sql server 2005, i configured the logshipping by using two instances of sql 2005 , instead of disabling the logshipping i deleted the jobs then again when i went to configure logshipping it is not possible i got an error of 14262.(email removed)

When you say “SELECT COUNT(*)” you are a different command: a SELECT that returns a single item, the COUNT, of the number of items. Because there is no list, the result comes out at 1 – the count itself.

as when you are trying to Execute “Select *”, you must specify table name in from Clause. because * awaits for Table to give outputs of Columns and Data. when you are trying to execute Select *, this * means what ?

You have to specify query or Table to take output. so you will get an error when you will try to execute only “Select * ”

now, the 2nd question is for : Select Count(*), it suppose to give you Count of Rows, it means if you try to Execute Select Count(1) or Select Count(*) or Select Count(Any Variable). then the output will be 1. same for all queries.

You can replace any value instead of * for the COUNT function.Ex

Select COUNT(5) will result as 1.

The error resulting from select * is obvious it expects an object where it can extract the result set.

the select * command returns all columns from all rows in the table.

if any data value in any row and/or column is corrupt or has a problem an error can be returned.

there is also a higher probability of a hardware problem from returning all the data from the table as select * does.

the select count(*) command only returns the count of rows in the table.

as the select count(*) command does not return any actual data from the table, data corruption will likely not impact the select (*) command.

have a nice weekend :-)

So, when we use ‘select *’ it definitely give and error because ‘*’ is meant to have all the fields but there is not any table and without table it can only raise an error.

So, in the case of ‘Select Count(*)’, there will be an error as a record in the count function so you will get the result as ’1′.

Try using : Select COUNT(‘RAMESH’) and think there is an error ‘Must specify table to select from.’ in place of ‘RAMESH’

Pinal : If i am wrong then please clarify this.

Thanks,
Ramesh Vagh,
Software Engineer