Question

How can I do with SQL Server to get a single row where the only non-null values are the ones that are consistent and non-null through all the selected rows.

 A    B     C     D
10   NULL  text  NULL
4    abc   text  NULL
4    def   text  NULL

Should give the following row:

 A    B     C     D
NULL NULL  text  NULL

Answer 1

declare @t table(A int, b varchar(10), c varchar(max), d int)

insert @t values(10, null, 'text', null)
insert @t values(4, 'abc', 'text', null)
insert @t values(10, 'def', 'text', null)


select case when max(rna) > 1 then null else min(a) end, 
case when max(rnb) > 1 then null else min(b) end, 
case when max(rnc) > 1 then null else min(c) end, 
case when max(rnd) > 1 then null else min(d) end 
 from 
(
select rna = rank() over(order by a),
rnb = rank() over(order by b),
rnc = rank() over(order by c),
rnd = rank() over(order by d),
a, b,c,d
 from @t
 ) e

If you have text columns replace the column type with varchar(max). Text columns are outdated.

Using count(distinct col1) was by first thought, but it doesn’t count null values.

select count(distinct a) from (select cast(null as int) a) b 

returns 0 rows