I have a table of messages:
id
sender_id
recipient_id
I want to pull all the messages of user (id:1) where he was either the sender or the recipient and JOIN the "other guy" he was talking to.
something like:
SELECT * FROM `message`
LEFT JOIN `user` AS u ON IF(sender_id != 1, sender_id = u.id, recipient_id = u.id)
WHERE sender_id=1 OR recipient_id=1
the reason I don't join both the sender and recipient is that I already have the user I'm searching on, so I think it's a waste to join him on every message - unless you tell me otherwise!
This query I got from another SO question, but I've read it's not efficient at all, so what will be a better query?
This would work:
SELECT *
FROM message
JOIN users ON (message.sender_id = 1 AND user.id = message.recipient_id)
OR (message.recipient_id = 1 AND user.id = message.sender_id)
Note that there are various other ways of doing this in a more performant fashion. This is the most straightforward method that I can see.
Your way could work but the join won't use an index. If you want a fast join you need something like joined_table_indexed_field = some_expression, for example:
SELECT *
FROM `message` m
JOIN `user` AS u ON u.id = IF(m.sender_id = 1, m.recipient_id , m.sender_id)
WHERE m.sender_id=1 OR m.recipient_id=1
In this case #Grim's solution is better because it doesn't rely on mysql to perform an union index_merge for the where clause.
You could try a union:
(
SELECT * FROM `message`
INNER JOIN `user` u ON u.id = recipient_id
WHERE sender_id = 1
) UNION (
SELECT * FROM `message`
INNER JOIN `user` u ON u.id = sender_id
WHERE recipient_id = 1
)
Related
I have 3 tables like so
Table 1: UserInfo
user_id userName
123 userOne
Table 2: Post
user_id postContent
123 This is test message
Table 3: LikePost
user_id likesPostId
123 This is test message
I would like to run a query to get total number of post likes, posts, and user information from those 3 tables.
I can do this for each one such as in Post table:
SELECT COUNT(*) FROM Post WHERE Post.user_id = '123'
and SELECT * FROM UserInfo WHERE UserInfo.user_id = '123'
Is anyone have better solution in just 1 query? Thank you so much!
Use a structured query (with subqueries) something like this.
SELECT u.user_id, u.userName, p.num postcount, l.num likecount
FROM UserInfo u
LEFT JOIN (
SELECT COUNT(*) num,
user_id
FROM Post
GROUP BY user_id
) p ON u.user_id = p.user_id
LEFT JOIN (
SELECT COUNT(*) num,
user_id
FROM LikePost
GROUP BY user_id
) l ON u.user_id = l.user_id
What's going on here? The two subqueries, for example
SELECT COUNT(*) num,
user_id
FROM LikePost
GROUP BY user_id
each generate a virtual table with either zero or one row per user_id, showing a count for each user_id. You then join those virtual tables to your UserInfo table.
Use LEFT JOIN because ordinary innner JOIN will suppress users that lack either posts or likes.
Try This
SELECT ui.userName,Count(p.*),
Count(lp.*) as TotalPostLikes
FROM UserInfo ui
INNER JOIN Post p on p.user_id=ui.user_id
INNER JOIN LikePost lp on lp.user_id=ui.user_id
WHERE ui.user_id = '123'
GROUP BY ui.userName
If you want to select Username, Post and Likes on post, try the following
SELECT ui.userName,p.postContent as PostContent,
(SELECT COUNT(lp.user_id) FROM LikePost lp
WHERE lp.user_id=ui.user_id) as Likes,
(SELECT COUNT(_p .user_id) FROM Post _p
WHERE _p .user_id=ui.user_id) as TotalPosts
FROM UserInfo ui
INNER JOIN Post p on p.user_id=ui.user_id
WHERE ui.user_id = '123'
Yes you can do it within one query using leftjoin on Post and LikePost like below
SELECT COUNT(*),User.userName FROM UserInfo as User
leftjoin Post as Post on Post.user_id = User.user_id
leftjoin LikePost as LikePost on LikePost.user_id = User.user_id
where Post.user_id = 123
group by Post.user_id
I have a table that stores all users connections ( date & ip ) and i want to retrieve with a single query all the users data (nickname , avatar ...) + the last record of my connections history table of this user ...
SELECT
*
FROM
`users`
LEFT JOIN
`connections_history` ON `users`.`id` = `connections_history`.`guid`
How i can proceed thx
Assuming that connections_history table has an AUTO_INCREMENT column id:
SELECT *
FROM (
SELECT u.*, MAX(h.id) as hid
FROM users u
LEFT JOIN connections_history h ON u.id = h.guid
GROUP BY u.id
) u
LEFT JOIN connections_history h ON h.id = u.hid
Unfortunately Mysql does not support window functions, you need Correlated sub-query to do this.
Try something like this
SELECT *
FROM users
LEFT JOIN connections_history ch
ON users.id = ch.guid
AND EXISTS (SELECT 1
FROM connections_history ch1
WHERE ch.guid = ch1.guid
HAVING Max(ch1.date) = ch.date)
One way is finding the rows with max date for each guid in subquery and then join with users table.
Like this:
select *
from `users` u
left join (
select *
from `connections_history` c
where date = (
select max(date)
from `connections_history` c2
where c.`guid` = c2.`guid`
)
) t on u.`id` = t.`guid`;
You can do this with a correlated subquery in the ON clause:
SELECT u.*, ch.*
FROM `users` u LEFT JOIN
`connections_history` ch
ON ch.`guid` = u.`id` AND
ch.date = (SELECT MAX(ch2.date)
FROM connections_history ch2
WHERE ch.guid = ch2.guid
);
This formulation allows the query to take advantage of an index on connections_history(guid, date).
I have 3 tables
users ( user_id , name )
thread ( thread_id , date_time)
subscribers ( subscriber_id , thread_id)
subscriber id is a foreign key from users table how can i get thread of 2 specefic users , i'm doing something like this but it's giving me blank rows
SELECT t.thread_id, s.subscriber_id, u.user_id
FROM subscribers s
LEFT JOIN thread t ON t.thread_id = s.thread_id
LEFT JOIN user u ON s.subscriber_id = u.user_id
WHERE s.subscriber_id = 1 AND s.subscriber_id = 2
You should check your query as #Tim Biegeleisen said.
I will highlight the portion of your query which is causing the empty set result:
WHERE s.subscriber_id = 1 AND s.subscriber_id =2
^ really?
You are asking MySQL to return records where the subscriber_id is both 1 and 2. This doesn't make any sense. In the corrected query below I have changed the WHERE condition to use OR instead of AND:
SELECT u.user_id, u.name, t.thread_id
FROM users u INNER JOIN susbscribers s ON u.user_id = s.subscriber_id
INNER JOIN thread t ON s.thread_id = t.thread_id
WHERE u.user_id = 1 OR u.user_id = 2
I have two tables as follows
user [ ID , username ]
relationship [ user1_id(FK) , user2_id (FK) , status ]
I am trying to get the username by using either user1_id or user2_id where the status = 1 from relationship table. user1_id and user2_id are both IDs from the user table. The following query is failing and I am not sure where it's going wrong.
SELECT
U.username,
(R.first_user_id, R.second_user_id AS friends)
FROM
user U,
`relationship` R
WHERE (R.`first_user_id` = {$userID} OR R.`second_user_id`)
AND (`status` = 1 AND U.ID = friends)
returns both names of users in a relationship with a status of 1.
this also assumes that if a relationship record exists, both users must be in the user table.
SELECT U1.UserName, U2.username
FROM Relationship R
INNER JOIN USER U1
on R.User1_ID = U1.user_ID
INNER JOIN USER U2
and R.User2_ID = U2.user_ID
WHERE R.Status=1
It looks like you may be trying to get the usernames of all users that have a relationship with a certain specified user, regardless of the order of user IDs in the relationship record. That could be this:
SELECT
U.username,
U.first_user_id,
FROM
user U
JOIN `relationship` R
ON R.first_user_id = U.ID
WHERE
(R.`second_user_id` = {$userID})
AND (`status` = 1)
UNION ALL
SELECT
U.username,
U.second_user_id,
FROM
user U
JOIN `relationship` R
ON R.second_user_id = U.ID
WHERE
(R.`first_user_id` = {$userID})
AND (`status` = 1)
If that produces duplicates (or could do) and you don't want it to do, then change the UNION ALL to a straight UNION.
I have succeeded based on xQbert answer:
SELECT
U1.username,
U2.username
AS user_friend
FROM
Relationship R
INNER JOIN
user U1
ON
R.first_user_id = U1.ID
INNER JOIN
user U2
ON
R.second_user_id = U2.ID
WHERE (R.`first_user_id` = {$userID} OR R.`second_user_id` = {$userID})
AND `status` = 1
I am trying to use the following code to get the 6 users with which the current user has most recently chatted. I have two problems. First of all, if the current user has recieved a message from the other user but has only sent, that other user isnt fetched. Second of all, the ORDER BY clause is causing an error. Im a beginner in SQL so I have no idea what's going on.
Thanks in Advance!
Here's the code:
SELECT users.*
FROM users INNER JOIN
messages fromuser
ON (fromuser.fromid = users.id) INNER JOIN
messages touser
ON (touser.toid = users.id)
WHERE fromuser.toid = :userid OR touser.fromid = :meid
GROUP BY users.id
ORDER BY MAX(messages.datetime)
LIMIT 6;
This should do your job, and it relies less on MySQL extensions than your other answer so far. I estimate that it would perform about the same, but it's surely wordier.
SELECT u.*
FROM (
SELECT DISTINCT otherid
FROM (
SELECT
m.fromid AS otherid,
MAX(m.datetime) as maxts
FROM messages m
WHERE m.toid = :userid
GROUP BY m.fromid
UNION ALL
SELECT
m.toid AS otherid,
MAX(m.datetime) as maxts
FROM messages m
WHERE m.fromid = :userid
GROUP BY m.toid
) um
ORDER BY maxts DESC
LIMIT 6
) otheru
INNER JOIN users u
ON u.id = otheru.otherid
Your logic is doomed to fail, because one users.id cannot be two different values at the same time. I think this query does what you want:
SELECT u.*
FROM messages m INNER JOIN
users u
ON (m.fromid = u.id AND m.toid = :userid) OR
(m.toid = u.id AND m.fromid = :userid )
GROUP BY u.id
ORDER BY MAX(m.datetime) DESC
LIMIT 6;
Notice that it joins to the users table by the id that is not the current user.