Question

Lets say I have table with ID int, VALUE string:

ID    |  VALUE
1        abc 
2        abc 
3        def
4        abc
5        abc
6        abc

If I do select value, count(*) group by value I should get

VALUE   | COUNT
abc       5
def       1

Now the tricky part, if there is count == 1 I need to get that ID from first table. Should I be using CTE? creating resultset where I will add ID string == null and run update b.ID = a.ID where count == 1 ?

Or is there another easier way?

EDIT:

I want to have result table like this:

ID      VALUE  count
null    abc    5
3       def    1

Answer 1

If your ID values are unique, you can simply check to see if the max(id) = min(id). If so, then use either one, otherwise you can return null. Like this:

Select Case When Min(id) = Max(id) Then Min(id) Else Null End As Id,
       Value, Count(*) As [Count]
From   YourTable
Group By Value

Since you are already performing an aggregate, including the MIN and Max function is not likely to take any extra (noticeable) time. I encourage you to give this a try.