Question

I’ve the below table

ID    TYPE    
---   ----    
1     P    
1     W    
2     P    
3     W    
4     W    
4     X    
5     P    
6     null  

I need a new table to be created like the one below

ID   Count of Type      Code    
--  --------------     -------    
1        2             null    
2        1             P      
3        1             W    
4        2             null    
5        1             P    
6        0             null    


1st col ---> ID    
2nd col ---> count of "type" for an ID    
3rd col ---> if count(type) = 1 then TYPE      
             else null    

Kindly help me in writing an ORACLE SQL query

Answer 1

You could use a subquery with the max function to get a value for the code and then use that in a case statement to get the value in your final query only when the count=1.

select id, cnt, case when cnt=1 then maxtype else null end as code
from 
(select id, count(*) as cnt, max(type) as maxtype
from t1
group by id) t2