I need to run a select statement that returns all rows where the value of a column is not distinct (e.g. EmailAddress).

For example, if the table looks like below:

CustomerName EmailAddress Aaron Christy Jason Eric John

I need the query to return:

Aaron Christy John

I have read many posts and tried different queries to no avail. The query that I believe should work is below. Can someone suggest an alternative or tell me what may be wrong with my query?

select EmailAddress, CustomerName from Customers group by EmailAddress, CustomerName having COUNT(distinct(EmailAddress)) > 1
0

7 Answers

This is significantly faster than the EXISTS way:

SELECT [EmailAddress], [CustomerName] FROM [Customers] WHERE [EmailAddress] IN (SELECT [EmailAddress] FROM [Customers] GROUP BY [EmailAddress] HAVING COUNT(*) > 1)
4

The thing that is incorrect with your query is that you are grouping by email and name, that forms a group of each unique set of email and name combined together and hence 

aaron and christy and john and

are treated as 3 different groups rather all belonging to 1 single group.

Please use the query as given below :

select emailaddress,customername from customers where emailaddress in (select emailaddress from customers group by emailaddress having count(*) > 1)
1
select CustomerName,count(1) from Customers group by CustomerName having count(1) > 1
1

How about

SELECT EmailAddress, CustomerName FROM Customers a WHERE Exists ( SELECT emailAddress FROM customers c WHERE a.customerName != c.customerName AND a.EmailAddress = c.EmailAddress)
0

Just for fun, here's another way:

;with counts as ( select CustomerName, EmailAddress, count(*) over (partition by EmailAddress) as num from Customers ) select CustomerName, EmailAddress from counts where num > 1
3

Rather than using sub queries in where condition which will increase the query time where records are huge.

I would suggest to use Inner Join as a better option to this problem.

Considering the same table this could give the result

SELECT EmailAddress, CustomerName FROM Customers as a Inner Join Customers as b on a.CustomerName <> b.CustomerName and a.EmailAddress = b.EmailAddress

For still better results I would suggest you to use CustomerID or any unique field of your table. Duplication of CustomerName is possible.

SELECT Title, Id FROM dbo.TblNews WHERE (Title IN (SELECT Title FROM dbo.TblNews AS TblNews_1 GROUP BY Title HAVING (COUNT(*) > 1))) ORDER BY Title
  • sort in title