Question

I have got the following query:

WITH data AS( 
    SELECT * FROM partstat WHERE id=4
)
SELECT id, AVG(Value) AS Average
FROM (
    SELECT id, 
    AVG(column_1) as column_1, 
    AVG(column_2) as column_2, 
    AVG(column_3) as column_3 
    FROM data
    GROUP BY id
) as pvt
UNPIVOT (Value FOR V IN (column_1,column_2,column_3)) AS u
GROUP BY id

if column_1,column_2 and column_3 (or one of this columns) have values then i get result as the following:

id, Average

4, 5.12631578947368

if column_1,column_2 and column_3 have NULL values then the query does not return any rows as the following:

id, Average

my question is how can i get as the following result if columns contents NULL values?

id, Average

4, NULL

Answer 1

Have you tried using COALESCE or ISNULL?

e.g.

ISNULL(AVG(column_1), 0) as column_1,   

This does mean that you will get 0 as the result instead of ‘NULL’ though – do you need null when they are all NULL?

Edit:

Also, is there any need for an unpivot? Since you are specifying all 3 columns, why not just do:

SELECT BankID, (column_1 + column_2 + column_3) / 3 FROM partstat
WHERE bankid = 4

This gives you the same results but with the NULL

Of course this is assuming you have 1 row per bankid

Edit:

UNPIVOT isn’t supposed to be used like this as far as I can see – I’d unpivot first then try the AVG… let me have a go…

Edit:

Ah I take that back, it is just a problem with NULLs – other posts suggest ISNULL or COALESCE to eliminate the nulls, you could use a placeholder value like -1 which could work e.g.

SELECT bankid, AVG(CASE WHEN value = -1 THEN NULL ELSE value END) AS Average 
FROM ( 
    SELECT bankid,  
    isnull(AVG(column_1), -1) as column_1 ,
    AVG(Column_2) as column_2 ,
    Avg(column_3) as column_3 
    FROM data     
    group by bankid
) as pvt 
UNPIVOT (Value FOR o in (column_1, column_2, column_3)) as u
GROUP BY bankid 

You need to ensure this will work though as if you have a value in column2/3 then column_1 will no longer = -1. It might be worth doing a case to see if they are all NULL in which case replacing the 1st null with -1