SQL query to select another row with minimum and maximum of nid value

Question

I have a 3 columns

nid aid cst
1    1   23
2    3   45
3    1   67
4    2   34
5    3   12
6    1   6

Please re-read for explanation: I have to find the cst of aid which has minimum value of nid for example whne i select aid=1 then it must give 23 as it correponds to mimimum value of nid(1) and when i select 3 it must give 45 as it has least nid(2) as compared to all other nids of aid

My try is this ad it do not work :

select cst from tbl 
where (nid) IN (select min(nid) from tbl) and aid=nid 

I also have to do the same for max as i done for min.

Answer 1

One method uses row_number() :

select t.*
from (select t.*, row_number() over (partition by aid order by cst) as seqnum
      from tbl t
     ) t
where seqnum = 1;

Your method would work with table aliases, qualified column names, and the correct logic:

select t.cst
from tbl t
where t.cst = (select min(t2.cst) from tbl t2 where t2.aid = t.aid);

Or, more simply:

select aid, min(cst)
from t
group by aid;

Answer 2

select cst
from tbl 
where aid=1 and nid=(select min(nid) from tbl where aid=1)

This query will give you minimum values of cst for all values of aid

Answer 3

select cst  from tbl_NID where aid =1 and  nid in ( select min (nid) from tbl_NID where aid=1  )

select cst  from tbl_NID where aid =1 and  nid like ( select min (nid) from tbl_NID where aid=1  )

Example Query