Consider this mysql tables structure (useful to store private/group chat messages):
USERS
user_id
username
password
GROUPS (= DISCUSSIONS / TOPICS)
group_id
name
GROUPS_MEMBERS (= MEMBERS OF A SPECIFIC DISCUSSION / TOPIC)
group_id
user_id
MESSAGES
message_id
timestamp
from_user_id
destination_type (enum - group, user)
destination_id
Can you please help me with the query to retrieve the list of the 5 more recent dicussions (either private or group) in which a specific user has been a active?
Important:
I don't have actual code since I'm just deciding how to structure the database tables. The table structure presented above it's pretty self-explanatory (destination_id is a reference to group_id, and group members are all the users that will receive a message. Finally, all messages sent between the users of a specific group make a discussion or topic).
Here is what I want to do (it's very easy... don't over-think it... it's like any chat/messaging system like Facebook or Gmail etc).
When a user logs in and opens the chat he will of course see all the latest discussion which he is/has been a part of. In a chronological DESC order.
So I need to write the query to retrieve the latest 5 GROUP_IDs (= discussions) in chronological DESC order. But only the discussions which the logged-in user is a part of.(Of course I have the id of the logged-in user.. for example 16)
P.s. I didn't build this table structure myself but it seems logic; the only problem is the one presented above.
Here's my suggestion. You can get different records by using DISTINCT and get only five records by using LIMIT. You can replace logged_in_user_id with the login id.
SELECT DISTINCT GROUPS.group_id FROM USERS
JOIN GROUP_MEMBERS ON USERS.user_id = GROUP_MEMBERS.user_id
JOIN GROUPS ON GROUPS.group_id = GROUP_MEMBERS.group_id
JOIN MESSAGES ON destination_type = 'group' AND destination_id = GROUPS.group_id
WHERE USERS.user_id = logged_in_user_id
ORDER BY timestamp DESC
LIMIT 5;
#Igor Carmagna:
I have gone through your question and according to that i think you are required list the top 5 messages which have been left by the end users right ?. So for that please please follow below given steps.
1) First and for most thing you are required to do is that Join.
2) In this step you are required to use max() function which will give you list of the users on the base of messages received. Now, according to your question you are required to have only top 5 records so you are bound use (max-5) function this will given top 5 records
Hope this will make you day !!
Cheers :) :P
Related
I know this has been covered somewhat but it hasn't helped my situation, rather there's been discrepancies in the rank. Wondering if anyone would be able to help!
So i have a game, the database tables are:
users, maps, nicknames, user_game_scores
Im developing a leader board and easily able to get the information ordered by score. fantastic.
But i want to rank this so that i can pull a specific users scores and the rank be relevant to all scores. eg:
GLOBAL SCORES
user info - Score - (rank)1
user info - Score - (rank)2
user info - Score - (rank)3
etc.
Whereas USER SCORES are more likely to be:
user info - Score - (rank)82
user info - Score - (rank)94
user info - Score - (rank)115
etc.
I imagine the implementation to be this:
SELECT users.first_name, users.surname, player_nicknames.nickname, maps.map_name, user_game_scores.score,
FIND_IN_SET( score, ( SELECT GROUP_CONCAT( score ORDER BY score DESC ) FROM user_game_scores ) ) AS rank
FROM `user_game_scores`
INNER JOIN users ON user_game_scores.user_id = users.user_id
INNER JOIN maps ON user_game_scores.map_id = maps.map_id
INNER JOIN player_nicknames ON user_game_scores.user_id = player_nicknames.user_id
WHERE user_game_scores.deleted is null
AND users.deleted is null
AND player_nicknames.deleted is null
ORDER BY user_game_scores.score DESC
But it returns this: (click here) - names etc have been removed from the image as it may not be appropriate to display
As you can see the Rank tends to miss a number or two (number 2 and 23). i understand that something like rank 24 will group and continue (which i prefer to happen in that instance) but i dont understand why some of the rank is missing and really dont want to post process this functionality.
Sorry this is long but i thought id provide as much information as i can. Thanks in advance!
It's probably because your SELECT GROUP_CONCAT subquery doesn't filter "deleted" (deleted is null) entries. – Paul Spiegel 9 hours ago
Scenario
I have three elements in this problem. One is an array of ids in this format: (1,3,5,6,8). That array is a list of id of users I want to display. The second element is table that contains user information something simple like: id name surname email. The third element is a second table that contains users configuration. There are two parameters in that last table, one is lid, and the other is usraction (among others, but the important are those two). lid represent a permission type and usraction the value, if the user wants his data to be public there will be a row on that table where lid=3 and usraction="accepted", also I register the datetime of the action every time the user changes this permission, so each time he change it a new row is added, and in order to retrieve the actual state of the permission i have to retrieve the last row for the user an check the value of usraction like this:
SELECT * FROM legallog WHERE uid = '.$user['id'].' AND lid = 3 ORDER BY ABS(`registration` - NOW()) LIMIT 1
Then in php:
if($queryresult && $queryresult[0]['usraction']=='accepted') //display data
The problem
In the scenario id described how im getting the actual state of the permission set by one user at the time, the problem now is I want to sort of clean an array of ids in one or two sql calls. Lets say I want to print the user information of 4 users, one function gives me the ids in this format: (2,6,8,1), but those users may not want to display their information, using the query I showed before I can make a call to the sql server for each user and then generate a new array, if the users who authorize are 1 and 8 the result array will be (8,1).
The think is whit an array of 100 users I will make 100 calls, and I dont want this, is there a way to solve this in one or two querys?
A query such as this gets you the information you want:
select u.*,
(select usraction from configuration c where c.userid = u.userid and c.lid = 3 order by datetime limit 1
) as lastLid3Action
from users u
where u.userid in (1,3,5,6,8)
If you only want "accepted" values, then make this a subquery:
select t.*
from (select u.*,
(select usraction from configuration c where c.userid = u.userid and c.lid = 3 order by datetime limit 1
) as lastLid3Action
from users u
where u.userid in (1,3,5,6,8)
) t
where LastLid3Action = 'Accepted'
As I understand you have two tables in the first table, where the user information is stored; and the second table, where the user permission is stored. And you want to get information from the first table using permission from the second table, then you need this query:
SELECT a.*
FROM first-table-name AS a
RIGHT JOIN second-table-name AS b a.uid = b.lid
WHERE uid in (1,3,5,6,8) AND usraction='accepted'
ORDER BY ABS)
LIMIT 1
You question is somewhat vague, but if you are asking how to select a number of records when you have a list of ids, the answer is:
select column, list, goes, here from tablename
where id in (1,5,8,12,413);
That will get you the values of the columns you list for just the records that match your array of ids.
Okay, so I want to have a news feed on my website. I have 3 tables named Users, Follow, and Posts. Basic user data goes into the Users table, who is following who is stored in the Follow table, and whatever the user posts goes into Posts. Now, I know how to select every post from a database table and limit it using the WHERE clause. But how would I write my query to select all all of the posts from only user's they are following, and display them by DESC date? Thanks.
Here's a general layout for you, make three tables like you mentioned, I've outlined below just as an example
[TABLES]
users
followers
posts
In the users table you should have at least columns like userid (auto incremented value / primary key).
The followers table should have something like userid which would match to the users table userid, a followid column which would also have the id # for the follower from the users table.
Then for your posts table you would want to have userid too so when each post is made it would have the id from users table.
Then you would need to do something like:
SELECT p.*
FROM posts AS p
WHERE p.userid IN (SELECT followid FROM followers WHERE userid = ###)
ORDER BY p.date DESC
Now it really depends on how you are getting the users id to figure this out. If your passing the users id using a session after they logged in similar to something like Facebook, then you could change userid = ### to something like userid = ".$_SESSION['userid']." But again it really depends on how you pass the users id but the above should at least get you somewhat started.
Make sure to put indexes on the userid, followid columns so that when the table becomes larger it will do the joins quickly.
An alternative to #Shane's answer is to use the JOIN operator:
'SELECT p.* // I prefer to name all the fields, but for brevity's sake I'll use the shorthand
FROM Posts AS p
INNER JOIN Follow AS f ON p.userid = f.followid
WHERE f.userid = '.$selectedUserID.'
ORDER BY p.date DESC;'
For an inputed User ID ($selectedUserID), it will find all User ID's of the people they follow (matching follow ID to user ID on the Follow x-ref table) and then find their respective posts from the Post table in descending order by date. It will return empty if they do not follow anyone or the people they follow have no posts.
I also hope I do not need to remind you to sanitize your input to the database and escape your output to the web.
Is this what you're looking for?
I'm trying to get a users position between the users friends, but I don't have any idea of how I can do this...
I have two tables.
Table 1: friends (where all the users friends are listed)
Table 2: users (where all the users are listed)
I want the query to check the users position between his friends.
So if I, for example have ID 1 (with 100 credits) and a friend with ID 2 (with 21 credits), the query would list my position as 1.
You don't really provide much information on your table layout, so it's going to be impossible for me to provide a very specific example. I'm also afraid I don't really understand your question, but I'll give it a shot...
First, I'll assume your users table has at least these columns:
id (PK)
credits
And that the friends table has these columns:
user (FK to users.id)
friend (FK to users.id)
Now, if I understand your question, you want to rank all of a user's friends, based on how many credits they have, so:
SELECT u.id,u.credits
FROM friends AS f
JOIN users AS us ON f.friend = u.id
WHERE f.user = 1
ORDER BY u.credits DESC;
in order to get the position I would recommend using PHP for this and not try to put it all in one query. So get a sorted list like Flimzy described and get the position by using an array function like array_search.
I have a social network similar to myspace/facebook. In my code you are either a person's friend or not a friend, so I show all actions from people you are friends with (in this post I will refer to actions as bulletin posts alone to make it easier to visualize.
So you every time a person post a bulletin it will show up to any person who is there friend.
In mysql you would get a persons friend list by doing something like this,
SELECT user_id FROM friends WHERE friend_id = 1 (user ID)
I want to know how a site like facebook and some others would show all bulletin post from your friends and from your friends' friends?
If anyone has an idea please show some code like what kind of mysql query?
The answer is that they aren't doing selects on a friend table, they are most likely using a de-normalized news-event table. We implemented a news-feed similar to Facebooks on DoInk.com, here's how we did it:
There is the notion of a "NewsEvent" it has a type, an initiator (a user id) and a target user (also a user id). (You can also have additional column(s) for other properties relevant to the event, or join them in)
When a user posts something on another users wall we generate an event like this:
INSERT INTO events VALUES (wall_post_event, user1, user1)
When viewing user1's profile, you'd select for all events where user1 is either the initiator or the target. That is how you display the profile feed. (You can get fancy and filter out events depending on your privacy model. You may consider doing this in memory for performance reasons)
Example:
SELECT * FROM events WHERE initiator = user1 or target = user1 //to see their profile feed
SELECT * FROM events WHERE initiator IN (your set of friend ids) //to see your newsfeed
When you want to see the newsfeed for all events relative to your friends you might do a query selecting for all events where the initiator is in your set of friends.
Avoid implementations with sub-selects, depending on the complexity, they will not scale.
you do a subquery:
SELECT DISTINCT user_id FROM friends WHERE friend_id IN
(SELECT user_id FROM friends WHERE friend_id = 1)
Test both of these for performance:
SELECT DISTINCT user_id
FROM friends f1
JOIN friends f2 ON f1.friend_id = f2.user_id
WHERE f2.friend_id = 1
and
SELECT DISTINCT user_id
FROM friends
WHERE friend_id IN (SELECT user_id FROM friends WHERE friend_id = 1)
Often they're the same but sometimes they're not.
Make sure friend_id and user_id are indexed.
The simple approach would be to do some kind of simple nested clause. So say you have a table with posts and the posters id, and a friends table, the first layer would be
SELECT post FROM posts JOIN friends
on post.userid = friends.friend_id
WHERE friend.id = 1 (user ID)
then to get a friends of friends
SELECT post FROM posts JOIN
(SELECT DISTINCT friends_2.friend_id FROM friends AS friends_1
JOIN friends as friends_2
on friends_1.friend_id = friends_2.id where friends_1.id = 1)
AS friends
wHERE post.userid = friends.friend_id AND mainid = 1 (user ID)
You can repeat this nesting each time you want to add another layer of friend abstraction. The problem with this approach is that it would take a very long time to execute. For every time you add a layer of friend abstraction you are increasing the complexity by a power of n (where n is the number of rows in your table).
It is more likely that they are saving the viewable friends in a table somewhere, so lets make a new tabled called friends_web
user_id, friend_id, level
when a user friends someone, it adds that new friend into friends_web at a level of 0(since that friend is no people away) then adds that friends friends at a level of 1 (since its 1 friend away). In order to keep the table integrity you would also want to add the inverted record. To clarify if A adds B as a friend and C is a friend of B, the following two records would get added to our new table
A, C, 1
C, A, 1
since now A can see C and C can see A.
now when we want a query we just do
SELECT post FROM posts
JOIN friends_web ON post.user_id = friends_web.friend_id
WHERE friends_web.user_id = user_id AND friends_web.level < 2 (or however deep you want to look)
by doing that you minimized your query complexity when doing post lookups while being able to look more then 1 layer deep into a friend web.
Sorry for the long winded response.
This should pull out all the user's friend's posts.
SELECT * FROM posts WHERE uid IN (SELECT friend_uid FROM friends WHERE uid=1) ORDER BY post_id DESC
This should pull out all posts that are your friend's friend's.
SELECT * FROM posts WHERE uid IN (SELECT friend_uid FROM friends WHERE uid IN (SELECT friend_uid FROM friends WHERE uid=1)) ORDER BY post_id DESC