How do I find duplicate rows, and at the same time distinct? - sql

Question

I have a SQL query question.
I have a table with first name, last name and mobile numbers of clients.
Thor Prestby 98726364
Thor Prestby 98726364
Lars Testrud 12938485
Lise Robol 12938485
I want to find rows with the same mobile number, that have different names. As you see above Thor has 2 rows, and that's right. Lars and Lise have the same mobile number and that is what I want to find.

Answer 1

You pretty much outlined yourself the actions needed to take in your question.
In a nutshell
use a subselect to get all the distinct rows
group on mobilenumber from this unique resultset from the subselect
retain only those mobilenumbers that occur at least twice
SQL Statement
SELECT mobilenumber, COUNT(*)
FROM (
SELECT DISTINCT mobilenumber, firstname, lastname
FROM YourTable
) AS q
GROUP BY
mobilenumber
HAVING COUNT(*) > 1

Answer 2

I am assuming that you are using MS SQL Server here but you could use:
Declare #t table
(
FirstName varchar(100),
LastName varchar(100),
Mobile bigint
)
Insert Into #t
values ('Thor','Prestby',98726364),
('Thor','Prestby', 98726364),
('Lars','Testrud',12938485),
('Lise','Robol', 12938485),
('AN','Other', 12345868)
Select Mobile
From #t
Group By Mobile
Having Count(*) > 1
EXCEPT
Select Mobile
From #t
Group By FirstName, LastName, Mobile
Having Count(*) > 1

Answer 3

SELECT * FROM the_table tt
WHERE EXISTS (
SELECT * FROM the_table xx
WHERE xx.mobineno = tt.mobileno
AND (xx.fname <> tt.fname OR xx.lname <> tt.lname)
);

Answer 4

For this records:
Thor Prestby 98726364
Thor Prestby 98726364
Lars Testrud 12938485
Lise Robol 12938485
AN Other 12345868
Try it:
select t.mobile, count(*) from new_table t
where t.mobile in
(select t1.mobile from new_table t1
where t1.mobile=t.mobile
group by t1.firstname, t1.lastname, t1.mobile
having count(*)=1)
group by t.mobile
having count(*)>1
You will get this result:
12938485 2

Answer 5

SELECT t1.phone, count(t1.phone) CountNo
FROM (SELECT distinct * FROM YourTable) t1
Left Outer Join YourTable t2 ON t1.phone = t2.phone AND ( t1.FirstName <> t2.FirstName OR t1.LastName <> t2.LastName)
WHERE t2.FirstName IS NOT NULL
GROUP BY t1.phone
HAVING count(t1.phone) > 1
ORDER BY CountNo desc

Answer 6

I am using standard SQL syntax and joins to achieve the results
Setup:
create table dummy
(
firstname varchar2(20),
lastname varchar2(20),
phone number
);
insert into dummy values('Thor','Prestby',98726364);
insert into dummy values('Thor','Prestby',98726364);
insert into dummy values('Lars','Testrud',12938485);
insert into dummy values('Lise','Robol',12938485);
Query:
select a.firstname,a.lastname,a.phone from dummy a inner join dummy b
on a.phone=b.phone and a.firstname != b.firstname and a.lastname != b.lastname;
Result
FIRSTNAME LASTNAME PHONE
-------------------- -------------------- ----------------------
Lise Robol 12938485
Lars Testrud 12938485