DISTINCT仅适用于一列，而另一列是随机的吗？

Question

I have one Table name Demodata which have two column col1 and col2. data of table is

col1   col2    
1        5  
1        6    
2        7    
3        8    
3        9    
4        10

and after SELECT command we need this data

col1    Col2    
1        5    
         6    
2        7   
3        8   
         9   
4        10

is this possible then what is query please guide me

Answer 1

Try this

    SELECT CASE WHEN RN > 1 THEN NULL ELSE Col1 END,Col2
    FROM
    (
    SELECT *,Row_Number() Over(Partition by col1 order by col1) AS RN
    From yourTable
    ) AS T

Answer 2

No it is not possible.

SQL Server result sets are row based not tree based. You must have a value for each column (alternatively a NULL value).

What you can do is grouping by col1 and run an aggregate function on the values of col2 (possibly the STUFF function).

Answer 3

You can do this in SQL, using row_number() :

select (case when row_number() over (partition by col1 order by col2) = 1
             then col1
        end), col2
from table t
order by col1, col2;

Notice that the ordering is important. The way you have written the result set, the data is ordered by col1 and then col2 . Result sets do not have an inherent ordering, unless you include an order by clause.

Also, I have used NULL for the missing values.

And, finally, although this can be done in SQL, it is often preferable to do these types of manipulations on the client side.

Answer 4

What do you want to select on the duplicates, an empty string, NULL , 0, ... ?

I presume NULL , you can use a CTE with ROW_NUMBER and CASE on col1 :

WITH CTE AS(
  SELECT RN = ROW_NUMBER() OVER (PARTITION BY col1 
                               ORDER BY (SELECT 1))
        , col1, col2
  FROM Demodata 
)
SELECT col1 = CASE WHEN RN = 1 THEN col1 ELSE NULL END, col2
FROM CTE

Demo