SQL Server 2014

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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 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);
1 rows affected

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);
1 rows affected

-- Method 1

SELECT
  id,
  median =
  (
    SELECT
      AVG(val)
    FROM
      (
        SELECT
          c   = COUNT(*) OVER (),
          rn  = ROW_NUMBER() OVER (ORDER BY v.val ASC),
          val = v.val
        FROM
          (
            VALUES
            (t.a), (t.b), (t.c), (t.d), (t.e), (t.f), (t.g),
            (t.h), (t.i), (t.j), (t.k), (t.l), (t.m), (t.n),
            (t.o), (t.p), (t.q), (t.r), (t.s), (t.t), (t.u)
          ) AS v (val)
        WHERE
          v.val IS NOT NULL
      ) AS derived
    WHERE
      rn IN ((c + 1) / 2, (c + 2) / 2)
  )
FROM
  temp AS t
;


id
median


1
5.000000

2
4.000000


-- Method 2

SELECT
  id,
  median = AVG(x.val)
FROM
  temp AS t
  CROSS APPLY
  (
    SELECT
      c   = COUNT(*) OVER (),
      rn  = ROW_NUMBER() OVER (ORDER BY v.val ASC),
      val = v.val
    FROM
      (
        VALUES
        (t.a), (t.b), (t.c), (t.d), (t.e), (t.f), (t.g),
        (t.h), (t.i), (t.j), (t.k), (t.l), (t.m), (t.n),
        (t.o), (t.p), (t.q), (t.r), (t.s), (t.t), (t.u)
      ) AS v (val)
    WHERE
      v.val IS NOT NULL
  ) AS x
WHERE
  x.rn IN ((x.c + 1) / 2, (x.c + 2) / 2)
GROUP BY
  t.id
;


id
median


1
5.000000

2
4.000000