Select duplicate persons with duplicate memberships - sql

Question

SQL Fiddle with schema and my intial attempt.
CREATE TABLE person
([firstname] varchar(10), [surname] varchar(10), [dob] date, [personid] int);
INSERT INTO person
([firstname], [surname], [dob] ,[personid])
VALUES
('Alice', 'AA', '1/1/1990', 1),
('Alice', 'AA', '1/1/1990', 2),
('Bob' , 'BB', '1/1/1990', 3),
('Carol', 'CC', '1/1/1990', 4),
('Alice', 'AA', '1/1/1990', 5),
('Kate' , 'KK', '1/1/1990', 6),
('Kate' , 'KK', '1/1/1990', 7)
;
CREATE TABLE person_membership
([personid] int, [personstatus] varchar(1), [memberid] int);
INSERT INTO person_membership
([personid], [personstatus], [memberid])
VALUES
(1, 'A', 10),
(2, 'A', 20),
(3, 'A', 30),
(3, 'A', 40),
(4, 'A', 50),
(4, 'A', 60),
(5, 'T', 70),
(6, 'A', 80),
(7, 'A', 90);
CREATE TABLE membership
([membershipid] int, [memstatus] varchar(1));
INSERT INTO membership
([membershipid], [memstatus])
VALUES
(10, 'A'),
(20, 'A'),
(30, 'A'),
(40, 'A'),
(50, 'T'),
(60, 'A'),
(70, 'A'),
(80, 'A'),
(90, 'T');
There are three tables (as per the fiddle above). Person table contains duplicates, same people entered more than once, for the purpose of this exercise we assume that a combination of the first name, surname and DoB is enough to uniquely identify a person.
I am trying to build a query which will show duplicates of people (first name+surname+Dob) with two or more active entries in the Person table (person_membership.person_status=A) AND two or more active memberships (membership.mestatus=A).
Using the example from SQL Fiddle, the result of the query should be just Alice (two active person IDs, two active membership IDs).
I think I'm making progress with the following effort but it looks rather cumbersome and I need to remove Katie from the final result - she doesn't have a duplicate membership.
SELECT q.firstname, q.surname, q.dob, p1.personid, m.membershipid
FROM
(SELECT
p.firstname,p.surname,p.dob, count(*) as cnt
FROM
person p
GROUP BY
p.firstname,p.surname,p.dob
HAVING COUNT(1) > 1) as q
INNER JOIN person p1 ON q.firstname=p1.firstname AND q.surname=p1.surname AND q.dob=p1.dob
INNER JOIN person_membership pm ON p1.personid=pm.personid
INNER JOIN membership m ON pm.memberid = m.membershipid
WHERE pm.personstatus = 'A' AND m.memstatus = 'A'

Answer 1

Since you are using SQL Server windows function will be handy for this scenario. The following will give you the expected output.
SELECT firstname,surname,dob,personid,memberid
from(
SELECT firstname,surname,dob,p.personid,memberid
,Rank() over(partition by p.firstname,p.surname,p.dob order by p.personid) rnasc
,Rank() over(partition by p.firstname,p.surname,p.dob order by p.personid desc) rndesc
FROM [StagingGRG].[dbo].[person] p
INNER JOIN person_membership pm ON p.personid=pm.personid
INNER JOIN membership m ON pm.memberid = m.membershipid
where personstatus='A' and memstatus='A')a
where a.rnasc+rndesc>2

Answer 2

You have to add Group by and Having clause to return duplicate items only-
SELECT
person.firstname,person.surname,person.dob
FROM
person, person_membership, membership
WHERE
person.personid=person_membership.personid AND person_membership.memberid = membership.membershipid
AND
person_membership.personstatus = 'A' AND membership.memstatus = 'A'
GROUP BY
person.firstname,person.surname,person.dob
HAVING COUNT(1) > 1