Finding the median of column values per row

I've tried the below query, but the median value shown is wrong.

Query

select 
(select cast(Avg(TotAvg * 1.0 )as decimal(6,2))
 from (values (convert(decimal(6,2), a)),(convert(decimal(6,2), b))
             ,(convert(decimal(6,2), c)),(convert(decimal(6,2), d))
             ,(convert(decimal(6,2), e)),(convert(decimal(6,2), f))
             ,(convert(decimal(6,2), g)),(convert(decimal(6,2), h))
             ,(convert(decimal(6,2), i)),(convert(decimal(6,2), j))
             ,(convert(decimal(6,2), k)),(convert(decimal(6,2), l))
             ,(convert(decimal(6,2), m)),(convert(decimal(6,2), n))
             ,(convert(decimal(6,2), o)),(convert(decimal(6,2), p))
             ,(convert(decimal(6,2), q)),(convert(decimal(6,2), r))
             ,(convert(decimal(6,2), s)),(convert(decimal(6,2), t))
             ,(convert(decimal(6,2), u))
    ) as Totalavg(TotAvg)
) as Median
from temp

Column values are a to u in a row.

Table Values

First row - 1,5,6,7,8,2,6,3,4,5,2,1,6,5,7,8,2,7,6,2,8
Second row - 1,5,6,7,8,2,2,3,2,4,2,1,4,5,9,8,2,7,6,2,8

Create table script

create table temp 
(
    id int identity(1,1),
    a decimal(6,2),
    b decimal(6,2),
    c decimal(6,2),
    d decimal(6,2),
    e decimal(6,2),
    f decimal(6,2),
    g decimal(6,2),
    h decimal(6,2),
    i decimal(6,2),
    j decimal(6,2),
    k decimal(6,2),
    l decimal(6,2),
    m decimal(6,2),
    n decimal(6,2),
    o decimal(6,2),
    p decimal(6,2),
    q decimal(6,2),
    r decimal(6,2),
    s decimal(6,2),
    t decimal(6,2),
    u decimal(6,2)
)

Insert Table Script

insert into temp
    (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u)
values
    (1,5,6,7,8,2,6,3,4,5,2,1,6,5,7,8,2,7,6,2,8)

insert into temp
    (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u)
values
    (1,5,6,7,8,2,2,3,2,4,2,1,4,5,9,8,2,7,6,2,8)

First step is to unpivot columns into rows. Then you can enumerate the values using row_number and pick the middlest value from there:

select id, avg(val)
from ( 
    select id, val
         , count(*) over (partition by id) as c
         , row_number() over (partition by id order by val) as rn
    from temp unpivot (
             val for col in (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u)
         ) as x 
) as y
where rn IN ((c + 1)/2, (c + 2)/2) 
group by id;

StackExchange Database Administrators Q#205808, answer score: 7