Average across multiple columns with varying data - sql

Question

I have 10 decimal columns and I would like to add a computed column to my table that contains the average of these 10. A complication is that not every record has all 10 columns filled in. Some records have 4 some have 8 and some have 10.
e.g.
ID D1 D2 D3 D4 D5 D6 D7 D8 D9 D10
1 12 19 13 14
2 32 53 34 54 65 34 12 09
3 41 54 33 61 71 12 09 08 08 12
How can I get the average of these where ID1 = 14.5, ID2 = 36.625 etc
I can't just do D1 + D2 + D3... / 10 as the 10 isn't always 10
The ideal would just be to do AVG(D1:D10) but clearly the world isn't ideal!

Answer 1

You can't use AVG aggregate function (because it works on rows) but you can calculate an average using the following query:
SELECT
(ISNULL(D1,0) + ISNULL(D2,0) +
ISNULL(D3,0) + ISNULL(D4,0) + ISNULL(D5,0) +
ISNULL(D6,0) + ISNULL(D7,0) + ISNULL(D8,0) +
ISNULL(D9,0) + ISNULL(D10,0)) /
CASE
WHEN
D1 IS NOT NULL
OR D2 IS NOT NULL
OR D3 IS NOT NULL
OR D4 IS NOT NULL
OR D5 IS NOT NULL
OR D6 IS NOT NULL
OR D7 IS NOT NULL
OR D8 IS NOT NULL
OR D9 IS NOT NULL
OR D10 IS NOT NULL
THEN
(
CASE
WHEN D1 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D2 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D3 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D4 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D5 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D6 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D7 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D8 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D9 IS NOT NULL THEN 1 ELSE 0
END +
CASE
WHEN D10 IS NOT NULL THEN 1 ELSE 0
END
)
ELSE 1
END
FROM yourtable

Answer 2

AVG for each id:
select id, avg(d) from
(
select id, id1 as d from tablename
union all
select id, id2 as d from tablename
union all
select id, id3 as d from tablename
union all
select id, id4 as d from tablename
union all
select id, id5 as d from tablename
union all
select id, id6 as d from tablename
union all
select id, id7 as d from tablename
union all
select id, id8 as d from tablename
union all
select id, id9 as d from tablename
union all
select id, id10 as d from tablename)
group by id

Answer 3

Use Values table valued constructor to unpivot the data then find average per ID. Try this
select id,avg(data) from Yourtable
cross apply
(values(D1), (D2), (D3), (D4), (D5), (D6) ,(D7), (D8), (D9) ,(D10)) cs (data)
group by id
Or if your want decimal values then use this.
select id,sum(data)/sum(case when data is not null then 1.0 else 0 end) from Yourtable
cross apply
(values(D1), (D2), (D3), (D4), (D5), (D6) ,(D7), (D8), (D9) ,(D10)) cs (data)
group by id