How to eleminate duplicate records from mysql query

Question

I have one application where I have to show user's activities. I am facing one problem regarding duplicate entry/activities. First of all I have describe my schema:

Table: UserFriends

CREATE TABLE `testDb`.`UserFriends` (
  `Pk` INT NOT NULL AUTO_INCREMENT,
  `Userid` INT NULL,
  `Friendid` INT NULL,
  PRIMARY KEY (`Pk`));

Table: UserActivities

CREATE TABLE `testDb`.`UserActivities` (
  `Pk` INT NOT NULL AUTO_INCREMENT,
      `Userid` INT NULL,
  `Friendid` INT NULL,
  `ActivityType` TINYINT(1) NULL,
  PRIMARY KEY (`Pk`));

Insert some dummy data into the tables.

INSERT INTO UserFriends(Userid, friendid )
values (7,105), (7,92)  

INSERT INTO UserActivities(Userid, friendid )
values (92, 1054), (105,2014), (92,105) 

I have one user (pk - 7) in UserFriends table with 2 friends (e.g. id no(s) 105 & 92). There is some activities which is done by user (eg.7) and its friends. User 92 has become friends with user 1054, user 105 has added user 2014 as a friend and user 92 and user 105 also become a friend. Now I have to show user 7 to his/her activities. I have create a query which is fined all activities of user itself as well as it's all friends. Here is the query :

select ua.pk activityid, 
    if(uf.Friendid = ua.userid, ua.userid, ua.Friendid) myfriend,       
    if(uf.Friendid = ua.Friendid, ua.Friendid, ua.Userid) friend_of_friend
from UserFriends uf 
inner join UserActivities ua on uf.Friendid = if(uf.Friendid = ua.userid, ua.userid, ua.Friendid)
where uf.userid = 7

and I have got result as follows :

activityid,   myfriend,   friend_of_friend
1,            92,         1054
2,            105,        2014
3,            105,        92
3,            92,         105

Please check result carefully, there is a duplicate records come for activity id 3 due to join. User 7 has two friends (eg. 92, 105), so it comes twice. I want only one records. I don't know how to remove/eliminate this records. My original query has 6-7 table join and activity table has about 600000 records and userfriend table as around 200000 records. so I have to consider performance too. Please anyone can help to me to solve this problem. thanks.

Answer 1

try add GROUP BY activityid

like that :

    where uf.userid = 7
    GROUP BY activityid

Answer 2

Can you check this query

select DISTINCT ua.pk activityid, 
    if(uf.Friendid = ua.userid, ua.userid, ua.Friendid) myfriend,       
    if(uf.Friendid = ua.Friendid, ua.Friendid, ua.Userid) friend_of_friend
from UserFriends uf 
inner join UserActivities ua on uf.Friendid = if(uf.Friendid = ua.userid, ua.userid, ua.Friendid)
where uf.userid = 7

I have used a distinct keyword before ua.pk.

Reference: http://www.w3schools.com/sql/sql_distinct.asp