Question

I have below table

Id          Stack
------------------
1             a
1             b
2             c
2             d

I want to get below table result.

Id          Stack
------------------
1             a
2             c

I use DISTINCT but it doesnot work
how can I do it ?
are there any solution by using group by?

Answer 1

CREATE table sampletb(id int, stack varchar(10));

INSERT into sampletb values(1,'a');
INSERT into sampletb values(1,'b');
INSERT into sampletb values(2,'c');
INSERT into sampletb values(2,'d');

SELECT * FROM sampletb;

id          stack
----------- ----------
1           a
1           b
2           c
2           d


SELECT id,
       stack,
       row_number() over (partition by id order by stack) as row_number
from   sampletb;

This query will give you result like this.

id          stack      row_number
----------- ---------- --------------------
1           a          1
1           b          2
2           c          1
2           d          2

Now making the above query as subquery and getting the columns having
row_number=1 will give the desire output you wanted.

select id,stack from 
       (
       SELECT id,
              stack,
              row_number() over (partition by id order by stack) as row_number 
       FROM   sampletb) x
where  x.row_number=1;

id          stack
----------- ----------
1           a
2           c