Hi I have a table called Users and a table called friends, friends table have two data types UserID and FriendID, (foreign key of both data types to primary key of the Users table),
I need to give an ID and find a list of that persons friends'name, I am not sure if I have designed the tables wrongly or I should rewrite the query.
my query is as following, (so far it just shows the details of first matched person)
SELECT Users.Name
FROM Users
WHERE Users.ID = SELECT Friends.UserID
FROM Friends,Users
WHERE Users.ID = (Select Users.ID
From Users
WHERE Users.Username = 'John')
Try this:
SELECT Users.Name FROM Users WHERE Users.ID IN -- Get names that belongt to ID's
(SELECT FriendID FROM Friends WHERE UserID = -- All ID's of the Friends of
(SELECT UserID FROM Users WHERE Name = 'John')) -- Johns ID
I've solved it by changing the first = to IN
is this you want to achieve ??
User
UserID (PK)
Name
Friend
FriendID (PK)
UserID (FK)
select User.Name from User u join Friend f on f.UserID = u.UserID where Name = 'John'
Related
So I have a list of ids(userId's) that was found using a sql command that I want to check with my friends table to see if they are indeed friends with myself, a userid I will provide with, and have a column that will represent if they are and also group them if they are my friend and not my friend.
Example:
List of userids:
1
2
3
Friends table:
-------
userId *the userid sending a friend request*
friendId *the userid receiving the friend request*
relationshipId *an unique id for the relationship*
initiated_by *the userid initiating the friend request*
status *whether or not the users are friends 'friends' or 'pending'*
sample friends table data
I tried creating a subquery that would first get the list of ids I want, and then tried to compare it with my friends table but couldn't quite put it together because the friends table is not bidirectional, meaning each row represents a relationship between 2 people with a status friends or pending
Use a CASE expression to get the friend of a person (i.e. pick either the userid or the friendid from the friends table).
As of MySQL 8 you can use a WITH clause to get this readable:
with friends_of_user_1 as
(
select case when userid = 1 then friendid else userid end as userid
from friends
where 1 in (userid, friendid)
and status = 'friends'
)
, friends_of_user_2 as
(
select case when userid = 2 then friendid else userid end as userid
from friends
where 2 in (userid, friendid)
and status = 'friends'
)
select
userid,
userid in (select userid from friends_of_user_2) as is_friend_of_user_2
from friends_of_user_1;
The same without WITH:
select
userid,
userid in
(
select case when userid = 2 then friendid else userid end as userid
from friends
where 2 in (userid, friendid)
and status = 'friends'
) as is_friend_of_user_2
from
(
select case when userid = 1 then friendid else userid end as userid
from friends
where 1 in (userid, friendid)
and status = 'friends'
) friends_of_user_1;
You can get all friends bidirectional, i.e. (a,b), (b,a), (a,c), (c,a), ... with a UNION query. If it is guaranteed that there exists no (b,a) in the table when there exists (a,b), then you can use UNION ALL, otherwise use UNION.
Then you can aggregate per user and see whether they are friends with user 1 and/or user 2:
with all_friends as
(
select userid as userid1, friendid as userid2 from friends status = 'friends'
union
select friendid as userid1, userid as userid2 from friends status = 'friends'
)
select
userid1,
sum(userid2 = 2) > 0 as is_friends_with_user_2
from all_friends
group by userid1
having sum(userid2 = 1) > 0 -- is friends with user 1
Use the alias of Friends a second time to get the reciprocal relationship
SELECT A.Name,...
FROM Users A
JOIN friends FA ON A.userID = FA.userID
LEFT JOIN friends FB ON FA.friedID = FB.userID
JOIN Users B on FB.userID = B.userID
...
So FA is the friends of A and FB is the friend relationship of B back to A.
I have these two table, sorry for not being able to embed it due to lack of reputation. Currently, I am trying to grab the id of the person who is not friend with the userId '1'.
For instance, in friendlist Table, it shows that user Id '1' is friend with userId '2' and '3'. However, he is not friend with userId '4' and '5'.
So I want to grab the userId of 4 and 5.
I tried to grab friendId and using operator '<>' to grab non-friend Id but it doesn't work.
May I know how to?
friendlist Table
registeredUser Table
You can use a statement like this one:
SELECT * FROM registeredUser WHERE userId NOT IN (SELECT friendId FROM friendlist WHERE userId = 1) AND userId != 1;
This will return all the users that are not friends with the user which has the userId 1.
For you referance:
select u.userId from registerUser u, friendlist f
where u.userId=f.userId and (f.friendId=4 or f.friendId=5);
I am making a social networking application and now i am trying to make the database for the application.
I have 2 tables user table and follower table. Table structure look like this
user table follower table
---------------- ----------------
userid (int) userid
username follower id
----------------
I am trying to list all followers of a user. I need the followers username in the result. I don't know how to do it. Any help would be much appreciated. thanks.
Assuming "follower id" (hopefully not the actual column name) is a foreign key reference to user(userid), a simple join query should suffice
SELECT u.userid, u.username
FROM `follower table` f
INNER JOIN `user table` u on f.`follower id` = u.userid
WHERE f.userid = :userid -- the ID of the user who's followers you're after
Im beginner in sql soo i have big problem with this "big" select for friends table in cometchat. Can somebody write it for me.
Cometchat is configured for friends table :
friends
toid fromid
id 2 1
id 1 2
and sql select for it:
$sql = ("select DISTINCT ".TABLE_PREFIX.DB_USERTABLE.".".DB_USERTABLE_USERID." userid, ".TABLE_PREFIX.DB_USERTABLE.".".DB_USERTABLE_NAME." username,
".TABLE_PREFIX.DB_USERTABLE.".".DB_USERTABLE_LASTACTIVITY." lastactivity,
".DB_AVATARFIELD." avatar, ".TABLE_PREFIX.DB_USERTABLE.".".DB_USERTABLE_USERID." link,
cometchat_status.message, cometchat_status.status
from ".TABLE_PREFIX."friends join ".TABLE_PREFIX.DB_USERTABLE." on ".TABLE_PREFIX."friends.toid = ".TABLE_PREFIX.DB_USERTABLE.".".DB_USERTABLE_USERID." left join cometchat_status on ".TABLE_PREFIX.DB_USERTABLE.".".DB_USERTABLE_USERID." = cometchat_status.userid ".DB_AVATARTABLE."
where ".TABLE_PREFIX."friends.fromid = '".mysql_real_escape_string($userid)."' order by username asc");
return &sql;
My Rails app have friendships table :
friendships
user_id friend_id
id 1 2
id 2 1
When i just change order it does not work. I think that this is to hard for me right now. In rails i just check which friendship has a user_id of my profile and i show it friend_is as a friend.
THis is generated SQL for standard cometchat settings with friend table:
select DISTINCT users.id userid,
users.name username,
users.current_sign_in_at lastactivity,
users.id avatar,
users.id link,
cometchat_status.message,
cometchat_status.status
from friends
join users on friends.toid = users.id
left join cometchat_status on users.id = cometchat_status.userid
where friends.fromid = '10'
order by username asc
i try to change table from friends to my fiendships and toid (on friend_id) and formid( on user_id) and and vice versa but still it doesnt work and i do not get friends list.
I have a database table called users with a primary key of user_id for each user.
I also have a table called friends with two fields, user_id and friend_user_id.
The user_id field is always the lowest of the two user_id's in order to avoid duplicate entries.
Say I have two users in mind, (lets say user id 1 and user id 4 although they could be anything).
How would I return all rows from the users table for users that are friends with user 1 and user 4 (i.e mutual friends)?
I will give you the recipe:
Find all friends of user 1
Find all friends of user 2
Intersect them and the result will be the mutual friends.
Much like this:
UPDATE: Here's the query:
select f.friend_user_id from friends f where f.friend_user_id in (
select friend_user_id from friends where user_id=<id_of_user_a>)
and f.user_id=<id_of_user_b>
The ids returned by above query will be the id of all the users that are mutual friends of user_a and user_b. If you want to get all the details (name, etc) about those users, then do this:
select f.friend_user_id,u.* from friends f inner join users u
on u.user_id=f.friend_user_id
where f.friend_user_id in (
select friend_user_id from friends where user_id=<id_of_user_a>)
and f.user_id=<id_of_user_b>
SELECT friends.friend_user_id FROM user, friends
INNER JOIN friends ON friends.user_id = user.user_id
WHERE user.user_id = 1
AND friend.friend_user_id
IN (SELECT friends.friend_user_id
FROM user, friends
INNER JOIN friends ON friends.user_id = user.user_id
WHERE user_id = 4)