MS-SQL Average Columns with NULL

Question

So I've got 3 different columns (basket 1, 2, and 3). Sometimes these columns have all the information and sometimes one or two of them are null. I have another column that I'm going to average these values into and save.

Is there a sleek/easy way to get the average of these three columns even if one of them is null? Or do I have to have a special check for each one being null?

Example data( ~~ is null)

- B1 - B2 - B3 - Avg
------------------------------
- 10 - 20 - 30 - 20
- 10 - ~~ - 30 - 20
- ~~ - 20 - ~~ - 20

How would I write the T-SQL to update my temp table?

UPDATE @MyTable
   SET Avg = ???

---

Answer: Thanks to Aaronaught for the method I used. I'm going to put my code here just in case someone else has the same thing.

WITH AverageView AS
(
    SELECT Results_Key AS xxx_Results_Key,
            AVG(AverageValue) AS xxx_Results_Average
    FROM @MyResults
        UNPIVOT (AverageValue FOR B IN (Results_Basket_1_Price, Results_Basket_2_Price, Results_Basket_3_Price)) AS UnpivotTable
    GROUP BY Results_Key
)   
UPDATE @MyResults
    SET Results_Baskets_Average_Price = xxx_Results_Average
    FROM AverageView
    WHERE Results_Key = xxx_Results_Key;

Answer 1

Assuming you have some sort of ID column, the most effective way is probably to use UNPIVOT so you can use the normal row-based AVG operator (which ignores NULL values):

DECLARE @Tbl TABLE
(
    ID int,
    B1 int,
    B2 int,
    B3 int
)

INSERT @Tbl (ID, B1, B2, B3) VALUES (1, 10, 20, 30)
INSERT @Tbl (ID, B1, B2, B3) VALUES (2, 10, NULL, 30)
INSERT @Tbl (ID, B1, B2, B3) VALUES (3, 10, NULL, NULL)

SELECT ID, AVG(Value) AS Average
FROM @Tbl
UNPIVOT (Value FOR B IN (B1, B2, B3)) AS u
GROUP BY ID

If you don't have the ID column, you can generate a surrogate ID using ROW_NUMBER:

;WITH CTE AS
(
    SELECT
        B1, B2, B3,
        ROW_NUMBER() OVER (ORDER BY (SELECT 1)) AS ID
    FROM @Tbl
)
SELECT ID, AVG(Value)
FROM CTE
UNPIVOT (Value FOR B IN (B1, B2, B3)) AS u
GROUP BY ID