Getting Warning: Null Value Is Eliminated by an Aggregate or Other Set Operation

Warning: Null value is eliminated by an aggregate or other SET operation in Aqua Data Studio

You would mostly be using COUNT to summarize over a UID. Therefore

COUNT([uid]) will produce the warning:

Warning: Null value is eliminated by an aggregate or other SET operation.

whilst being used with a left join, where the counted object does not exist.

Using COUNT(*) in this case would also render incorrect results, as you would then be counting the total number of results (ie parents) that exist.

Using COUNT([uid]) IS a valid way of counting, and the warning is nothing more than a warning. However if you are concerned, and you want to get a true count of uids in this case then you could use:

SUM(CASE WHEN [uid] IS NULL THEN 0 ELSE 1 END) AS [new_count]

This would not add a lot of overheads to your query.
(tested mssql 2008)

Getting warning: Null value is eliminated by an aggregate or other SET operation

Mostly you should do nothing about it.

• It is possible to disable the warning by setting ansi_warnings off but this has other effects, e.g. on how division by zero is handled and can cause failures when your queries use features like indexed views, computed columns or XML methods.
• In some limited cases you can rewrite the aggregate to avoid it. e.g. COUNT(nullable_column) can be rewritten as SUM(CASE WHEN nullable_column IS NULL THEN 0 ELSE 1 END) but this isn't always possible to do straightforwardly without changing the semantics.

It's just an informational message required in the SQL standard. Apart from adding unwanted noise to the messages stream it has no ill effects (other than meaning that SQL Server can't just bypass reading NULL rows, which can have an overhead but disabling the warning doesn't give better execution plans in this respect)

The reason for returning this message is that throughout most operations in SQL nulls propagate.

SELECT NULL + 3 + 7 returns NULL (regarding NULL as an unknown quantity this makes sense as ? + 3 + 7 is also unknown)

but

SELECT SUM(N)
FROM   (VALUES (NULL),
               (3),
               (7)) V(N) 

Returns 10 and the warning that nulls were ignored.

However these are exactly the semantics you want for typical aggregation queries. Otherwise the presence of a single NULL would mean aggregations on that column over all rows would always end up yielding NULL which is not very useful.

Which is the heaviest cake below? (Image Source, Creative Commons image altered (cropped and annotated) by me)

After the third cake was weighed the scales broke and so no information is available about the fourth but it was still possible to measure the circumference.

+--------+--------+---------------+
| CakeId | Weight | Circumference |
+--------+--------+---------------+
|      1 | 50     | 12.0          |
|      2 | 80     | 14.2          |
|      3 | 70     | 13.7          |
|      4 | NULL   | 13.4          |
+--------+--------+---------------+

The query

SELECT MAX(Weight)        AS MaxWeight,
       AVG(Circumference) AS AvgCircumference
FROM   Cakes 

Returns

+-----------+------------------+
| MaxWeight | AvgCircumference |
+-----------+------------------+
|        80 |          13.325  |
+-----------+------------------+

even though technically it is not possible to say with certainty that 80 was the weight of the heaviest cake (as the unknown number may be larger) the results above are generally more useful than simply returning unknown.

+-----------+------------------+
| MaxWeight | AvgCircumference |
+-----------+------------------+
|         ? |          13.325  |
+-----------+------------------+

So likely you want NULLs to be ignored, and the warning just alerts you to the fact that this is happening.

Warning: Null value is eliminated by an aggregate or other SET operation

Use ISNULL

select jm.jobmst_id, ISNULL(max(tj.trgjob_order), 0) from jobmst jm

Your complete script

declare @eventname VARCHAR(64)
declare @eventid INT
set @eventname = 'event123'
set @eventid = (select tm.trgmst_id from trgmst tm where tm.trgmst_name = @eventname)
declare @trgjobmax INT
set @trgjobmax = (select max(trgjob_id) from trgjob)
declare @jobid TABLE (jobmst_id INT, trgjob_order INT)
insert into @jobid (jobmst_id, trgjob_order)
select jm.jobmst_id, ISNULL(max(tj.trgjob_order), 0) from jobmst jm
left outer join trgjob tj on tj.jobmst_id = jm.jobmst_id
inner join workgrp wg on wg.workgrp_id = jm.jobmst_owner
where wg.workgrp_name in  ('group1', 'group2', 'group3')
      and jm.jobmst_type = 2 and jm.jobmst_dirty <> 'X' and jm.jobmst_id
NOT IN (
select tj.jobmst_id from trgjob tj
where tj.trgmst_id = @eventid
)
group by jm.jobmst_id
order by jm.jobmst_id desc

Getting fixed T-SQL for Warning: Null value is eliminated by an aggregate or other SET operation

That's a lot of code.

I notice this line:

sum( 
    CASE 
    WHEN  (invoicedate >= dateadd(wk, datediff(wk, 0, getdate())-1, 0) 
    and invoicedate <= DATEADD(wk, DATEDIFF(wk, 6, CURRENT_TIMESTAMP), 6)) 
    THEN (ordhl.NetPrice*ordhl.shippedquantity/ 
    coalesce(ordhl.UnitOfMeasurePriceFactor,1)/ 
    coalesce(ordh.CurrencyRate,1))
    ELSE Null 
 END) lastweeksales

I suggest you change ELSE Null to ELSE 0, as long as it doesn't introduce divide by zero errors

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