SQL Query JOIN or IN operator? - sql

Question

I have two tables,
PERSON
and FRIENDS.
FRIENDS has the fields NAME and SURNAME.
A person has N friends.
I want to retrieve all the PERSONs that have atleast two FRIENDs, one with name ="mark", and the other with name="rocco" and surname ="siffredi".
Example: if I have a person that has 5 friends, one of them is called mark and no one is called rocco siffredi, no tables are returned.
I was thinking about:
SELECT * FROM person p
JOIN friends AS f ON p.ID=f.personID
WHERE f.name ="mark" AND f IN
( SELECT * from FRIENDS WHERE name="rocco" and surname="siffredi")
or
SELECT * FROM person p
JOIN friends AS f1 ON p.ID=f1.personID
JOIN friends AS f2 ON p.ID=f2.personID
WHERE f1.name="mark" AND f2.name="rocco" AND f2.surname="siffredi"
What is the best way? I mean the fastest way to execute it.
I don't care about readability.
Is there any other way to execute this query?
Ty.
EDIT: added the join on the ID...

Answer 1

I had to guess your column names and make up a table:
Use EXISTS:
CREATE table FRIENDS(person_id INT, friend_id INT)
go
SELECT *
FROM person
WHERE
EXISTS
(SELECT *
FROM friends f
JOIN person per
ON f.friend_id = per.id
WHERE
per.name ='mark' AND
person.id = f.person_id) AND
EXISTS
(SELECT *
FROM friends f
JOIN person per
ON f.friend_id = per.id
WHERE
per.name = 'rocco' AND
per.surname='siffredi' AND
person.id = f.person_id)

Answer 2

Your schema design isn't very good for what you are trying to do... I would have a Person table as you have, which would also contain a unique identifier called PersonId. I would then have a Friends table which took two fields - Person1Id and Person2Id.
This gives you a couple of important advantages - first of all your system is able to handle more than one bloke called John Smith (because we join on Ids rather than Names...). Secondly, a person's details are only ever recorded in the Person table. One definition of truth...

Answer 3

With these data as input:
INSERT INTO Person VALUES
(1, 'Bob', 'Smith'),
(2, 'Jim', 'Jones')
INSERT INTO Friends VALUES
(1, 1, 'Mark', 'Tally'),
(2, 1, 'John', 'Smith'),
(3, 1, 'Jack', 'Pollock'),
(4, 2, 'Mark', 'Rush'),
(5, 2, 'Rocco', 'Siffredi'),
(6, 2, 'Mark', 'Bush')
you can use this query:
SELECT PersonId, COUNT(*) AS NoOfFriends
FROM (
SELECT DISTINCT PersonId, Name,
Surname = CASE WHEN NAME = 'Mark' THEN NULl
ELSE Surname
END
FROM Friends
WHERE Name = 'Mark' OR (Name = 'Rocco' AND Surname = 'Siffredi') ) t
GROUP BY PersonId
to get the distinct number of required friends per PersonID:
PersonId NoOfFriends
------------------------
1 1
2 2
You can now join with the above table expression on PersonId and filter it by NoOfFriends:
SELECT p.*
FROM Person AS p
INNER JOIN (
SELECT PersonId, COUNT(*) AS NoOfFriends
FROM (
SELECT DISTINCT PersonId, Name,
Surname = CASE WHEN NAME = 'Mark' THEN NULl
ELSE Surname
END
FROM Friends
WHERE Name = 'Mark' OR (Name = 'Rocco' AND Surname = 'Siffredi') ) t
GROUP BY PersonId ) s ON s.PersonId = p.ID
WHERE s.NoOfFriends = 2
so as to get only persons having the required combination of associated friends:
ID Name Surname
-------------------
2 Jim Jones
P.S. I have completely re-written my answer after #t-clausen.dk's comment.