Trying to write a query that will display duplicates results as null - sql

Question

I have a table that looks like the first example.
I'm trying to write a MSSQL2012 statement that that will display results like the second example.
Basically I want null values instead of duplicate values in columns 1 and 2. This is for readability purposes during reporting.
This seems like it should be possible, but I'm drawing a blank. No amount of joins or unions I've written has rendered the results I need.
| Col1 | Col2 | Col3 |
+------+------+------+
| 1 | 2 | 4 |
| 1 | 2 | 5 |
| 1 | 3 | 6 |
| 1 | 3 | 7 |
+------+------+------+
| Col1 | Col2 | Col3 |
+------+------+------+
| 1 | 2 | 4 |
| Null | null | 5 |
| null | 3 | 6 |
| null | null | 7 |
+------+------+------+

Answer 1

I would do this with no subqueries at all:
select (case when row_number() over (partition by col1 order by col2, col3) = 1
then col1
end) as col1,
(case when row_number() over (partition by col2 order by col3) = 1
then col2
end) as col2,
col3
from t
order by t.col1, t.col2, t.col3;
Note that the order by at the end of the query is very important. The result set that you want depends critically on the ordering of the rows. Without the order by, the result set could be in any order. So, the query might look like it works, and then suddenly fail one day or on a slightly different set of data.

Answer 2

Using a common table expression with row_number():
;with cte as (
select *
, rn_1 = row_number() over (partition by col1 order by col2, col3)
, rn_2 = row_number() over (partition by col1, col2 order by col3)
from t
)
select
col1 = case when rn_1 > 1 then null else col1 end
, col2 = case when rn_2 > 1 then null else col2 end
, col3
from cte
without the cte
select
col1 = case when rn_1 > 1 then null else col1 end
, col2 = case when rn_2 > 1 then null else col2 end
, col3
from (
select *
, rn_1 = row_number() over (partition by col1 order by col2, col3)
, rn_2 = row_number() over (partition by col1, col2 order by col3)
from t
) sub
rextester demo: http://rextester.com/UYA17142
returns:
+------+------+------+
| col1 | col2 | col3 |
+------+------+------+
| 1 | 2 | 4 |
| NULL | NULL | 5 |
| NULL | 3 | 6 |
| NULL | NULL | 7 |
+------+------+------+