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Should I include the same function which I have used in the select in the group by?

Posted on 2011-03-02
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Last Modified: 2012-05-11
Should I include the same function which I have used in the select in the group by?

Select Coalesce(CountryID,1), Count(1)
From Tbl1
Group BY CountryID

Or should I script it as

Select Coalesce(CountryID,1), Count(1)
From Tbl1
Group BY (CountryID,1)

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Question by:Mr_Shaw
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6 Comments
 
LVL 4

Assisted Solution

by:MarioAlcaide
MarioAlcaide earned 100 total points
ID: 35016110
The second option looks better to me
0
 
LVL 22

Accepted Solution

by:
Thomasian earned 760 total points
ID: 35016124
Actually, they could return different results so it depends on what you need.

Here's an example
DECLARE @tbl1 table (CountryID int)
INSERT @tbl1
SELECT 1
UNION ALL SELECT NULL
UNION ALL SELECT NULL

SELECT coalesce(CountryId,1) id, COUNT(1) [count]
from @tbl1
group by countryid
/*
id	count
1	2
1	1
*/

SELECT coalesce(CountryId,1) id, COUNT(1) [count]
from @tbl1
group by coalesce(CountryId,1)
/*
id	count
1	3
*/

Open in new window

Note that in the first query, there are 2 records with id=1, while it was combined on the second query.
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LVL 17

Assisted Solution

by:Barry Cunney
Barry Cunney earned 380 total points
ID: 35016129
Yes second option
Select Coalesce(CountryID,1), Count(1)
From Tbl1
Group BY COALESCE(CountryID,1)

By using this any records with NULL value for CountryID will be given a 1 and the data will be grouped on this 1 as opposed to trying to group by NULL

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LVL 50

Assisted Solution

by:Lowfatspread
Lowfatspread earned 380 total points
ID: 35016240
yes your group by should contain the coalesce...

but it does depend as thomasian demonstrates what your really trying to achieve...


Select coalesce(country,1) as country,thecount
from (
select country,count(*) as thecount
from tbl1
group by country
) as x
order by 1
 
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LVL 15

Assisted Solution

by:Aaron Shilo
Aaron Shilo earned 380 total points
ID: 35027756
yes you should

the coalesce takes care of you null values.
AGG function diregard Null values.

if you dont use the Function then the results will be worng.
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Author Closing Comment

by:Mr_Shaw
ID: 35034853
thanks
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