I'm building a site that requires sharing with either group(s) or individual user(s). I know for a fact that google does not use mysql, but i was wondering how i could replicate such feature on my site. On g+, one can:
Share a post with the "public" (everyone can see it).
Share a post with "all circles" (everyone in your circles can see it).
Share a post with both circles and individual users. E.g. post = "my first post" and is shared with family,friends, user 1(Joey tribbiani), user 2 (Ross geller) etc.
Conditions:
If a post is shared with a circle and a new user is added to the circle, then (s)he should be able to see all the previous posts shared with that circle.
If a user is removed from a circle. (s)he cannot see posts shared with that circle except posts (s)he has commented on.
Currently my database tables look like this.
Circle_category
Cat_id
Cat_name
user_id
Posts
post_id
user_id
post
is_public
all_circle
Post_to_circle
entry_id
post_id
cat_id
Post_to_user
entry_id
post_id
user_id
Post a user in family circle(which is in Circle_category with cat_id of 1 ) can see
They can see posts that are public.
They can see posts shared with all circles.
They can see posts shared with family circle.
They can see posts shared with them (Individual user).
SQL
SELECT p.* FROM posts p
JOIN Post_to_circle pc
ON p.post_id = pc.post_id
JOIN Post_to_user pu
ON p.post_id = pu.post_id
WHERE p.is_public = 1
OR all_circle = 1
OR pc.cat_id = $cat_id
OR pu.user_id = $user_id
Quetions:
Firstly, I've been able to get posts from case 1(see all public post), case 2 (Posts shared with all circles) but the other 2 cases do not work. I thought about it and saw that the main problem is that i specified the where clause to get posts where p.is_public = 1 which means it neglets rows where p.is_public = 0. How do i update the query so it shows posts covering all four cases and also covers the conditions we talked about at the beginning.
Secondly, is there a better way to structure my tables? i'm not sure i'm doing it the right way.
From a quick read trough, all i can say is:
you are using a join statement instead of a left join statement.
using join means:
keep all rows from the table used in from-clause that validate true for the condition specified in that join clause.
since you are using 2 statements, the first join throws away all the records that dont have the needed join, the second join throws away all the records that dont have the needed join in the second one, but it only uses records that matched the first join.
you should use left join instead. this keeps all rows from the first table. all rows that didnt have a match, get the values NULL for the columns specified in the joined table(s)
simple example:
users table:
user_id
name
user_posts
post_id
user_id
content
created
related queries:
select *
from users u
JOIN user_posts up on up.user_id = u.user_id and up.created > date_sub(curdate(), interval 1 day)
this will use all users and make match with each post that was created less then a day ago by that user.
if the user didnt have a post in the last day, he will NOT be in the resultset.
change this example to
select *
from users u
LEFT JOIN user_posts up on up.user_id = u.user_id and up.created > date_sub(curdate(), interval 1 day)
this will use all users and make a match with each post that was created less then a day ago by that user
if the user hasn't posted in the last day, he will STILL be in the resultset, but all the columns from the posts table will be NULL
the where filters all the rows you have left after the joins. (mysql will use where clauses before joining, if they can speed up the query).
altering your query:
make sure the clauses in where statement are wrapped between () for all the different cases. ALSO this is NOT the complete answer, as there is info missing (example user tables, circle relation tables, friend relations)
also the all_circles option confuses me, so it's missing from the query, but this should get you on the right track
SELECT p.* FROM posts p
left JOIN Post_to_circle pc
ON p.post_id = pc.post_id and /* define statement for valid circles for user you're trying to get the posts for */
left JOIN Post_to_user pu
ON p.post_id = pu.post_id and /* define statement for valid friends for user you're trying to get the posts for */
WHERE
/* 1 day old */
p.created > date_sub(curdate(), interval 1 day)
AND (
/* is public */
p.is_public = 1 OR
/* or to friends */
pu.id is not null OR
/* or to circles */
pc.id is not null
)
Also, i'm suspecting you'll need 2 subqueries, which is not the best thing to do, and my advise would be to find all correct ids for the friends, and all ids for the valid circles and then using an IN clause in each join statement (part thats in comment)
Related
I have a chat system. There are 3 tables:
data_chats - holds the IDs of the chats themselves. This is where you mark a chat as deleted.
data_chat_parties - holds the member or team ID that is included in chat along with chat permissions, who they were invited by, etc
data_chat_messages - holds the actual messages of chats
With my query, I am trying to fetch the info from data_chat_parties related to the party requesting this information (ie currently logged in user), but also get the total number of chat parties in the chat.
SELECT
data_chats.id AS chat,
data_chats_parties.*,
COUNT(data_chats_parties.id) AS total_parties,
data_chats_messages.created AS last_message_created,
data_chats_messages.author AS last_message_author,
data_chats_messages.author_type AS last_message_author_type,
data_chats_messages.message AS last_message
FROM data_chats
LEFT JOIN data_chats_parties ON data_chats_parties.chat=data_chats.id
LEFT JOIN data_chats_messages ON data_chats_messages.chat=data_chats.id AND data_chats_messages.active=1
WHERE
data_chats.active=1 AND
data_chats_parties.member=1 AND
data_chats_parties.status >= 1
GROUP BY data_chats_parties.chat
ORDER BY last_message_created DESC
This all works fine, except that total_chat_parties always returns 1, presumably because it's only matching the record of data_chats_parties.member=1. How would I fetch the party record specific to this user but at the same time, fetch the total number of parties for this chat?
You should use a correlated query :
SELECT data_chats.id AS chat,
(SELECT COUNT(data_chats_parties.id) FROM data_chats_parties
WHERE data_chats_parties.chat = data_chats.id) AS total_parties,
data_chats_messages.created AS last_message_created,
data_chats_messages.author AS last_message_author,
data_chats_messages.author_type AS last_message_author_type,
data_chats_messages.message AS last_message
FROM data_chats
LEFT JOIN data_chats_messages
ON data_chats_messages.chat = data_chats.id
AND data_chats_messages.active = 1
AND data_chats_parties.member = 1
AND data_chats_parties.status >= 1
WHERE data_chats.active = 1
ORDER BY last_message_created DESC
Another thing is the conditions on the WHERE clause, you can filter the RIGHT table of a LEFT JOIN in the WHERE clause, those condition should only be specified in the ON clause.
You also group by a column from the RIGHT table - this is not suggested at all! Either use an inner join, or group by another field.
you may be able to use a subquery in the select statement to give you the desired count.
(select COUNT(data_chats_parties.id) from data_chats_parties where data_chats_parties.chat=data_chats.id) AS total_parties,
Also you can then remove the line
LEFT JOIN data_chats_parties ON data_chats_parties.chat=data_chats.id
Hopefully I've typed that all correctly =)
Let's imagine I have a databases with two tables, Users and Posts. The first table contains a row for each user, the second table a row for each post that users have written. If I want to display a post count on the users' profiles, which of these two strategies work the best:
Every time a user creates a post I UPDATE the Users table, +1 a field PostCount;
When someone visits the profile I simply run a select statement to get a count of post, for example SELECT COUNT(post_id) FROM Posts WHERE id_user = 100;
In the first case I have to UPDATE a table very often, which it could be bad as I believe a table gets locked when doing the update; in the second case I have to run a count every time the user visits a profile. Which poison is the less bitter? Is there any other way?
I would say that it depends on how many times you will display PostCount, especially for a huge amount of Users. If you are going to display it for 1000+ users on a page that will be called a lot of times, then the first solution should be the best. But you need to do transactions to be sure both tables Posts and Users are updated when adding a new post.
Otherwise, the second solution should be enough, but you should use LEFT OUTER JOIN so that you would get both information from Users and Posts table in only one query. Eg:
SELECT *
FROM Users u
LEFT OUTER JOIN (
SELECT user_id , COUNT(*) AS posts_count
FROM Posts
GROUP BY user_id
) p ON p.user_id = u.id
WHERE u.id = :searched_id
(And anyway you should use a Cache system so that you don't have to do the same SQL query for a same page if shown to several users.)
I'm having some problems retrieving data from two tables and then listing them. I'd like to list the user's feed posts and their likes activity all in one.
Feeds - Table for users posts
Likes - Table for users likes (So when a use likes a post, a record is added to likes (Table likes contains data which contains the feeds ID of the post liked)
What I'm attempting to make: List BOTH feeds and user's Like activity in an ACTIVITY WALL.
So it should output like (ordered by timestamp desc):
"THIS IS A POST by user A"
Shows that user C liked user B's post
"THIS IS A POST by user B"
"THIS IS A POST by user L"
Shows that user A liked user F's post
"THIS IS A POST by user F"
-and it goes on-
My current SQL:
SELECT * FROM feeds,likes WHERE feeds.deleted!=0 or likes.deleted!=0 ORDER BY feeds.timestamp, likes.timestamp
However, my problem is I have no idea how to link both tables, since the IDs in my 'feeds' differ from those in 'likes'
To combine the two sets, you can use a UNION ALL set operator.
Something like this:
SELECT f.timestamp AS `timestamp`
, 'feed' AS `src`
, f.feed_id AS `id`
, f.feed_content AS `content`
FROM feeds f
WHERE f.deleted!=0
UNION ALL
SELECT l.timestamp AS `timestamp`
, 'like' AS `src`
, l.like_id AS `id`
, l.note AS `content`
FROM likes l
WHERE l.deleted!=0
ORDER BY 1 DESC
Note the the queries (on either side of the UNION ALL operator) need to match, in terms of the number of columns returned, and the datatype of each column.
To accommodate differences, such as extra columns returned from one table, but not from the other, you can add literal expressions in place of the "missing" columns.
The return of the extra src column is one way we can use to distinguish which query a row was returned by. It's not mandatory to return such a column, but it's something I often find useful. (The src column could be removed from each query, if it's not useful for your use case.)
Note that it's also possible to combine the results from more than two queries in this way, we'd just add another UNION ALL and another query.
The column names in the combined resultset are determined from the first query. The column names and aliases in the second query are ignored.
The ORDER BY applies to the entire set, and follows the last select.
Query should be linked via postID
F=feeds table, L=likes table, U1=usertable linked to owned feeds, U2=usertable linked to likes table
SELECT F.postTitle+' posted by '+ U1.username,'liked by'+U2.username
FROM likes L
LEFT JOIN feeds F on (F.postID=L.postID)
LEFT JOIN users U1 on (U1.userID=F.userID)
LEFT JOIN users U2 on (U2.userID=L.userID)
ORDER BY L.date,L.postID DESC
When you write SELECT * FROM feeds,likes... you are implicitly CROSS JOINing both tables. The engine will combine every record in each table with every record in the other. That is far from what you want.
I don't think you should be "linking" both tables, either. What you need, roughly speaking, is to get every post and every like, and then order that big set according to timestamps.
It sounds more like a UNION between two queries, and an ORDER BY applied to the whole UNION. UNIONs are never easy on the eye, by the way...
The thing with UNIONs is that both sub-queries need to return the same amount of columns. Not knowing exactly which columns you have, I'll show you one possible solution:
SELECT activity, timestamp FROM (
( SELECT CONCAT(u.name,' posted ',f.content) as activity, timestamp
FROM user u
JOIN feed f on (f.user_id=u.id)
WHERE f.deleted!=0
) UNION
( SELECT CONCAT(u.name, ' liked a post by ',u2.name) as activity, timestamp
FROM user u
JOIN likes l on (l.user_id=u.id)
JOIN feed f on (l.feed_id=f.id)
JOIN user u2 on (f.user_id=u2.id)
WHERE l.deleted!=0
)
) as whole_result
ORDER by timestamp desc
You should, of course, modify this to match your structure.
Hope this helps!
I think, it's better to use 3rd table, say, "actions", and insert to it real actions. Then just select rows from this table, joined to "posts" & "users" table.
When user posts articles, o likes an article, insert corresponding row to "actions" table.
actions table:
|id|action_name|user_id|post_id| date |
1 posted 3 3 5/7/2014
2 liked 5 3 5/7/2014
3 liked 4 3 6/7/2014
4 posted 5 6 7/7/2014
5 liked 3 6 7/7/2014
SELECT user_name a, post_title b, action_name c FROM actions c LEFT JOIN users a ON a.id=c.user_id LEFT JOIN posts b ON b.id = c.post_id ORDER BY c.date DESC LIMIT 10
Then, in loop, choose how to display this data, according to "action_name".
In such way you can expand your wall for other activities, +use indexes for better database performance.
I am creating some sort of a social media like facebook and I'm trying to get the number of likes a post has using the following query.
SELECT posts.object_ID, posts.user_ID, posts.datetime, posts.text,
COUNT(likes.object_ID) AS likes,
SUM(IF(likes.user_ID=?, 1, 0)) AS allowLike, users.first_name,
users.last_name, userinfo.image_ID
FROM posts
LEFT JOIN users ON users.ID=posts.user_ID
LEFT JOIN friends ON (friends.user_ID_1=? OR friends.user_ID_2=?)
AND friends.approved=1
LEFT JOIN userinfo ON users.ID=userinfo.user_ID
LEFT JOIN likes ON likes.object_ID=posts.object_ID
WHERE ". $str ."
GROUP BY posts.object_ID
ORDER BY posts.datetime DESC
LIMIT 0,30
The value of $str is just a mechanism to filter out friends and stuff, e.g.:
$str = "(posts.user_ID=friends.user_ID_1 OR posts.user_ID=friends.user_ID_2) OR posts.user_ID=? ";
What happens now is that COUNT(likes.object_ID) returns 4 and SUM(IF(likes.user_ID=?, 1, 0)) returns 4 as well.
This, surprisingly enough, is the actual amount of likes times the number of friends I have(4), I assume, since a post with 2 likes shows up as 8 likes. Yesterday I had 3 friends and it showed up as 3. And it's only happening when the post is my own.
I use a very similar query for fetching the comments, yet nothing strange is happening there.
Any ideas?
EDIT: It is not just limited to my own posts. I just found a case where it is in someone elses post. Still, it is NOT happening to every post... which is weird. Also, it is not bound to my own likes...
EDIT2: Upon 'reliking' the post I was speaking about in EDIT1, it showed up as one, and after a couple of refreshes it still showed up as 1 like. Weird..
Your problem may be related to your WHERE clause. A parameter is not parsed; your WHERE is simply a long varchar, your RDMS is interpreting this as TRUE.
Well, I decided to give up on this, and just go for a solution similar to the one described by myself and #Duniyadnd in the comments on my question.
I have a table objects. It only contained an ID. I added a field 'likes'. And created two triggers: One for the newLike, and one for a deletedLike which would update the likes column at the given object_ID.
Now my query is as such:
SELECT
posts.object_ID, posts.user_ID, posts.datetime, posts.text, objects.likes,
SUM(IF(likes.user_ID=?, 1, 0)) AS allowLike, users.first_name, users.last_name,
userinfo.image_ID
FROM posts
LEFT JOIN users ON users.ID=posts.user_ID
LEFT JOIN friends ON (friends.user_ID_1=? OR friends.user_ID_2=?) AND friends.approved=1
LEFT JOIN userinfo ON users.ID=userinfo.user_ID
LEFT JOIN objects ON objects.ID=posts.object_ID
LEFT JOIN likes ON likes.object_ID=posts.object_ID
WHERE ". $str ."
GROUP BY posts.object_ID ORDER BY posts.datetime DESC LIMIT 0,30
So I cleared my likes table to start over, yet, allowLike (SUM(IF(likes.user_ID=?, 1, 0))) still returns 4. There is only 1 entry in the likes table, I'm still curious why this is hapenning? Again, I have 4 friends.
Or would I better place this in a new question.
The joins are causing multiple intermediate rows to be created from the cross joins of the rows in one table with those of another table. Therefore your 4 friends are causing the 1 like to be turned into 4 intermediate rows, and then it is summed up to get a result of 4.
Instead of all the joins, try using a select within the first select, like this query on posts/comments/likes:
select postid, postmessage,
(select count(commentid) from comment where post.postid = comment.postid) as numcomments,
(select sum(value) from like where post.postid = like.postid) as popularity
from post
group by postid
(I have like.value as being 1 or -1 as up votes and down votes)
Hope that helps :)
I'm trying to get the users full activity throughout the website.
I need to Join many tables throughout the database, with that condition that it is one user.
What I currently have written is:
SELECT * FROM
comments AS c
JOIN rphotos AS r
ON c.userID = r.userID
AND c.userID = '$defineUserID';
But What it is returning is everything about the user, but it repeats rows.
For instance, for one user he has 6 photos and 5 comments
So I expect the join to return 11 rows.
Instead it returns 30 results like so:
PhotoID = 1;
CommentID = 1;
PhotoID = 1;
CommentID = 2;
PhotoID = 1;
CommentID = 3;
and so on...
What am i doing wrong?
What I'm trying to achieve (example)
If you're a facebook user, every profile has a 'wall' which states the user's activity on the website in chronological order. I'm trying to make something similar.
What am i doing wrong?
you are using one complex query when you could use two simple ones.
You should do it as follows:
SELECT * FROM user AS u
LEFT JOIN rphotos AS r ON u.userId = r.userID
LEFT JOIN comments AS c ON u.userId = c.userID
WHERE u.userId = '$defineUserID'
Updated to fix silly mistakes
What this does is select all relevant users from the user table (1 in this case) then join in the other tables where necessary and shouldnt repeat rows.
The query also makes more sense when you think about it logically.
That you get 30 results if a specific user has 6 photos and 5 comments is quite normal, since you're just fetching the cartesian product of all photos and comments based on user ID. The table structure could shed some light onto possible solutions, but if the comments are related to the photos and you want to fetch all photos and the comments a specific user posted you might use something like :
SELECT * FROM rphotos p
LEFT JOIN comments c on c.photoID = p.photoID
WHERE p.userID = '$defineUserID' OR c.userID = '$defineUserID';
Personally I would split this into 2 queries and display the results separately because mixing them doesn't make any sense to me, ie. use
SELECT * FROM rphotos p
WHERE p.userID = '$defineUserID';
and
SELECT * FROM comments c
WHERE c.userID = '$defineUserID';
edit based on comment
If the ID fields are of the same type you could use something like
select actionID, relatedID, creationDate from
(
select 1 as actionID, photoID as relatedID, creationDate from rphotos
where userID = '$defineUserID'
union
select 2 as actionID, commentID as relatedID, creationDate from comments
where userID = '$defineUserID'
) actions
order by creationDate desc;
The actionID will be 1 for a photo, 2 for a comment and using the relatedID field you could lookup the linked data (if you need it, otherwise you could just drop it from the query).
BTW You probably want to filter the results further (ie. based on date) to prevent joining lots of rows in the union that you won't display...