Aggregate function error in SQL Server 2008 R2

Question

I want to retrieve the empId that belongs to more than one city. So I use this query:

select empId 
from phone 
group by city 
having  count(city) > 1

but I get an error:

Msg 8120, Level 16, State 1, Line 1
Column 'phone.empId' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Answer 1

Use GROUP BY and HAVING count distinct city to find empId's with more than 1 city:

SELECT empId
FROM phone
GROUP BY empId
HAVING COUNT(DISTINCT city) > 1

Answer 2

该错误的意思是，如果您要使用GROUP BY子句，那么在SELECT语句中，您只能“选择”要分组的列并在该列上使用聚合函数，因为其他列将不会出现在结果表中。

Answer 3

You can use ROW_NUMBER() also to work it :
following code should work :

select empId from 
(
select distinct empId,city,ROW_NUMBER() over(partition by empId order by city) rn
 from phone 
 ) a
 where rn>1