NULL Aggregates

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NULL Aggregates

Steve Jones - SSC Editor

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January 6, 2015 at 10:53 pm

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Hany Helmy SSChampion Points: 13921 More actions · Answer 1

Good back to basics question, thanx.

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Hany Helmy
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Koen Verbeeck SSC Guru Points: 259085 More actions · Answer 2

Nice question, but I'd argue GROUPING doesn't ignore NULL values as well.

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manik_anu SSCrazy Points: 2377 More actions · Answer 3

wow... +1.. nice question.. thanks...

I had little remembrance of Count.

Using SELECT COUNT(*) or SELECT COUNT(1) (which is what I prefer to use) will return the total of all records returned in the result set regardless of NULL values.

Using COUNT(<Specific Column Name Here>)will count the number of non-NULL items in the specified column (NULL fields will be ignored).

Manik
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Rune Bivrin SSCrazy Eights Points: 8437 More actions · Answer 4

Not fond of this question.

COUNT(*) counts NULL:s, but COUNT(<expression>) doesn't.

select count(*), count(a)

from (values (1), (NULL)) x(a)

And GROUPING most certainly considers NULL:s.

Just because you're right doesn't mean everybody else is wrong.

Carlo Romagnano SSC-Insane Points: 22596 More actions · Answer 5

Rune Bivrin (1/7/2015)
Not fond of this question.
COUNT(*) counts NULL:s, but COUNT(<expression>) doesn't.
select count(*), count(a)
from (values (1), (NULL)) x(a)
And GROUPING most certainly considers NULL:s.

+1

🙂

Vimal Lohani SSCommitted Points: 1650 More actions · Answer 6

doubt on this question.

Review once again.. :-):-):-)

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Michael Riemer SSCertifiable Points: 5190 More actions · Answer 7

I can see where all the doubt in this question arises - as discussed. Only saving grace is the statement in the Aggregate Function link, which states:

Except for COUNT, aggregate functions ignore null values.

.

However even reading the information in the link for COUNT, you get the following:

COUNT(*) returns the number of items in a group. This includes NULL values and duplicates.
COUNT(ALL expression) evaluates expression for each row in a group and returns the number of nonnull values.
COUNT(DISTINCT expression) evaluates expression for each row in a group and returns the number of unique, nonnull values.

My guess the problem then is that for all other aggregate functions, it isn't possible to ignore null at all, however with COUNT you have an option based on the execution of the query. Most of the remaining aggregate functions cant be used generically (with *) and so by design have to either include or exclude nulls. The default then is to ignore them.

Koen Verbeeck SSC Guru Points: 259085 More actions · Answer 8

Michael Riemer (1/7/2015)
I can see where all the doubt in this question arises - as discussed. Only saving grace is the statement in the Aggregate Function link, which states:
Except for COUNT, aggregate functions ignore null values.
.

That statement is incorrect, GROUPING does not ignore null values. It will return a value (0 or 1) even if there is a NULL in the source data.

You can argue though if GROUPING is an aggregate function...

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Neil Burton SSC-Insane Points: 22905 More actions · Answer 9

Koen Verbeeck (1/7/2015)
Nice question, but I'd argue GROUPING doesn't ignore NULL values as well.

That's what I took from BOL and got the question wrong.

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vijaygodishala69 SSC Rookie Points: 49 More actions · Answer 10

Count(*) only count the NULL value but Count(<expression>) doesn't count the NULL value

P. K. Jat SSC Veteran Points: 236 More actions · Answer 11

good question...

but i have some doubt .

i think count(*) and grouping both are not ignoring null values and count(exp) ignoring null values.

Ed Wagner SSC Guru Points: 287024 More actions · Answer 12

I also clicked COUNT right away, then paused and thought about GROUPING. I actually looked it up and saw that I didn't ignore NULLs. Guessing between the two correct answers, I chose poorly. It's not a big deal, just debatable.

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Xavon SSCrazy Points: 2280 More actions · Answer 13

I wonder how MS is defining 'ignore'; because I would argue that if SUM ignored NULLs, I would not have to use half as many ISNULL(<column>, 0) statements.