I have a "users" table like this:
+-----+------------+---------+---------------+
| uid | first_name | surname | email |
+-----+------------+---------+---------------+
1 joe bloggs joe#test.com
2 bill bloggs bill#test.com
3 john bloggs john#test.com
4 karl bloggs karl#test.com
and a "connections" table like this:
+----+---------+----------+--------+
| id | user_id | user_id2 | status |
+----+---------+----------+--------+
1 1 3 1
2 3 1 1
3 4 3 1
4 3 4 1
5 2 3 1
6 3 2 1
Here id is auto auto_increment user id is saved in either user_id or user_id2. Status 1 means connection is approved and active.
Now I want to send an email alert to users with profile suggestion like Facebook or LinkedIn do. I assume it is possible to get mutual connections between users but not sure how to do. I have tried but it is not perfect. I want to get these all with one mysql query with user and their suggested connection profile. Any idea how to do this?
Many thanks in advance!
Such algorithms are never perfect: you can never know exactly if two people know each other. People might live in the same building, go to the same work, have 100 friends in common and even share the same hobbies without knowing each other (of course the odds are not that great).
What Social networks do exactly is of course unknown (that's part of the way they make money). But some aspects are known. For instance the number of mutual friends are important (together with for instance location, interests, hobbies, education, work, surname,...).
Based on what you provide, one can more or less only use the number of mutual friends. This can be done using the following query:
SELECT a.user_id, b.user_id2, count(*) --Select the two ids and count the number of transitive relations
FROM connections as a, connections as b --Use the table twice (transitivity)
WHERE a.user_id2 = b.user_id -- Transitivity constraint
AND a.user_id < b.user_id2 -- Maintain strict ordening (can be dropped when checked)
AND a.status = 1 -- First relation must be confirmed.
AND b.status = 1 -- Second connection must be confirmed.
AND NOT EXISTS ( -- Not yet friends
SELECT *
FROM connections as c
WHERE c.user_id = a.user_id
AND c.user_id2 = b.user_id2
)
GROUP BY a.user_id, b.user_id2 -- Make sure we count them correctly.
As you can see here, the fiddle calculates that (1,2), (1,4) and (2,4) are not yet friends, and all have one mutual friend.
Once the number of mutual friends surpasses a certain threshold, one can propose friendship.
I would however advice you to make your table more compact: add a CHECK to the table such that user_id is always strictly less than user_id2 (CHECK(user_id < user_id2)). This makes the database more compact, for most implementations of a database tool faster as well and queries will become simpler. What is after all the difference between (1,3,1) and (3,1,1).
Related
I have been searching for a good day for a way to search for a user that is in each category AND the next not OR.
user_id
-------
1
2
3
4
table_user_categories
user_id|category_id
-------------
1 |1
1 |2
2 |1
2 |3
So I want to ask MySQL, who is in category 1 AND 2. I have tried the IN(1,2) approach but this, as I understand it is OR not AND giving me the results of user_id 1 and 2 not just 1.
Its also quite important for this to be extensible as it can be as there are about 15 categories, so i'll need to add more into the query the more the user selects in my interface.
Huge apologies for anything I've missed in my post here, always easier to think of these things as opposed to asking.
I just dug out an old version of what I was trying - was just going to post this to compare...
SELECT u.user_id, COUNT(*) AS category_count
FROM table_user_categories AS u
WHERE u.category_id IN (1,2)
GROUP BY u.user_id
HAVING category_count = 2;
If you want to find all the user_ids that have both (or, generally, all) the given categories, you can use aggregation with filtering:
select user_id
from table_user_categories
where category_id in (1, 2)
group by user_id
having count(distinct category_id) = 2;
The having in above clause make sure that only user_id with both category_id 1 and 2 are returned.
I run a management system where people who work different shifts are registered.
I'd like to be able to make a display of how many times each worker/volunteer worked same shifts, like this:
|Amy|Carl|Max|
|---|----|---|
Amy | X | 2 | 6 |
Carl| 2 | X | 5 |
Max | 6 | 5 | X |
I was hoping you had some ideas how to form the query.
The only idea I've come up with so far is to make PHP create a custom query for each user.
Select count(common between user 1 and 2), count(common between user 1 and ...)
Select count(common between user 2 and 1), count(common between user 2 and ...)
etc..
I consider this an ugly way to do it and I am hoping there is some way of retrieving this data within a single query.
The database is stored like this:
Shifts
ID
From
To
Working
ID
ShiftID
UserID
Users
ID
Name
You'll have to self-join the Working table:
SELECT a.UserID, b.UserID, count(a.ShiftID) AS common_shifts
FROM Working AS a
INNER JOIN Working AS b ON ((a.ShiftID = b.ShiftID) AND (a.UserID <> b.UserID))
HAVING common_shifts > 0
Couldn't you do a cross join where each row is compared to the other, and handle the case of userid=userid to put an X instead?
I have created a database and website that will be used by football managers to select their team etc. Once a match has been completed events will be stored in the match_players table. Such events are Goal, Yellow Card, Red Card etc. I have no problem getting this information into php from SQL db.
I need to add up how many times a Goal appears (a '1' is placed in the SQL table) and for what team so that a final score can be displayed. So, for example, if Team A has 1 goal and Team B has 2 then I need to display that. I am trying to count the amount of times that a Goal is registered in the table. Any help will be greatly appreciated.
You can use MYSQL SUM
select SUM(Goal) from match_players where Team="A"
Or you can get the same for all teams by
select Team,SUM(Goal) from match_players group by Team
Why don't you demand this sum to SQL directly?
SELECT SUM(goals)
FROM match_table
WHERE team = 'Barcellona'
This should be much faster also than elaborate all data at "php-level"
If you want this detail for all teams
SELECT team,SUM(goals)
FROM match_table
GROUP BY team
Well if you store a 1 each time a goal is scored, your table looks like this:
TeamID goal
1 1
2 1
1 1
3 1
2 1
2 1
1 1
So you just want a count of how many times a team appears in that table:
select TeamID, count(*) from table group by TeamID
Will give you
TeamID | count(*)
1 | 3
2 | 3
3 | 1
Alright, I'm not the best with JOIN's and after all these years of working with mySQL you think I would be by now at the least minimally decent. Guess I've never really worked on anything superbly complex til now worth needing to join a table. So here I am, confused ever so slightly in need of a helpful example to get me on a roll, something that's pertinent to my actual data that I can make heads or tales of cause all the reading I'm doing online else where just gives me headaches for the moment. I think I might be stuck on the mythology of JOIN's being a hard thing to do, they don't seem like it but when ever I've tried I fail. So anyway I am working with PHP as my server side coding, and I believe MySQL 5.
So heres the construct to an extent.
I have table information and table connections.
Connections has: member_id, connection_id, active
Information has: firstname, lastname, gender, member_id
I should say the tables contain more data per table, but as I understand it I need write a query that I can use the member_id as the connector/foreign key. Where I can use both sides of the information. I need to know if active is 1, and then I need to know all of the columns above mentioned for information.
I tried
SELECT member_id,
connection_id,
active,
firstname,
lastname,
gender,
member_id
FROM connections, information
WHERE connection.member_id = information.member_id AND
connection.active = 1
and I've tried
SELECT * FROM connections, information
WHERE connection.member_id = information.member_id AND
connection.active = 1
With the first one I get member_id is ambitious which is understandable to a point i think cause of the matching columns between the two tables. Then the second query doesn't server me well as it only results with one person.
My Ultimate goal is to find all the connections for a specific member_id in the connections table, while gathering all the information about those connections from the information table using the connection_id as its the same thing as the member_id in the in the information table.
So in laymans terms if I am not making sense lets say I wanted to list out all my friends in from the DB. My connection table lets me know which people I am connected to where member_id is my id and connection_id is my friends member_id on another table. Hopefully that makes more sense. And this is where I am having trouble with my query and trying to write it correctly. If I could get a working sane sample of that I think I might be able to make better sense of JOIN's doesnt help that I also can't figure out what type of JOIN is best suited for my needs either I suppose.
EDIT....
Ok as per request from comment below. Sample data expected output from tables that look similar to this:
Connections Table
member_id, connection_id, active
1 | 2 | 1
1 | 3 | 1
1 | 4 | 1
1 | 5 | 1
2 | 1 | 1
2 | 5 | 1
3 | 1 | 1
Information Table
member_id, firstname, lastname, gender, ...other unimportant rows for this query
1 | Chris | Something | m | ....
2 | Tony | Something | m | ....
3 | Brandon | Something | m | ....
4 | Cassie | Something | f | ....
5 | Jeff | Something | m | ....
6 | John | Something | m | ....
now from the connections table I need to gather all the connection_id's associated with my member_id where active is 1 then from the information table gather everyone firstname, lastname, gender.. Now I know I can do this 2 step where I pool all the connection_id's from connections then run them through a loop of some sort and one by one get the resulting id's from the first query but to me that seems a bit obscure and process intensive which I want to avoid, which brings me here.. Currently from my original query posted to the many shared thus far trying to help my results are to the effect of
1 | Chris | Something | m | 2
1 | Chris | Something | m | 3
1 | Chris | Something | m | 4
1 | Chris | Something | m | 5
what I'd like to see returned is something like
2 | Tony | Something | m
3 | Brandon | Something | m
4 | Cassie | Something | f
5 | Jeff | Something | m
After looking at this I suppose I would also need to know the friendID column that matches my member_id as well but thats something to figure out after this initial hurdle
The error is in your WHERE Clause because instead of Connections you wrote it Connection which then the server generates the error.
...
WHERE connection.member_id = information.member_id AND
connection.active = 1
try this:
SELECT a.Member_ID,
a.FirstName,
a.LastName, a.gender,
b.Connection_ID
FROM Information a INNER JOIN Connections b
on a.Member_ID = b.Member_ID
WHERE b.`Active` = 1
UPDATE
if that's the case then you will most likely have a SELF JOIN
SELECT DISTINCT b.Connection_ID,
c.*
FROM Information a INNER JOIN Connections b ON
a.Member_ID = b.Member_ID
INNER JOIN Information c ON
b.Connection_ID = c.Member_ID
WHERE b.`Active` = 1
AND a.Member_ID = 'ID HERE' -- If you want to get for specific member
The error in the first is "ambiguous" not ambitious. Ambiguous means that the SQL engine doesn't know which column you are talking about, because you have two columns with the same name (different tables but still).
You can fix that by specifying the table name along with the column name where you list the columns for select.
For example
SELECT connections.member_id, connection_id, active, firstname, lastname, gender, information.member_id FROM connections, information WHERE connections.member_id = information.member_id AND connections.active = 1
The problem with returning only one suggests that there is only one record that matches your query but it's hard to guess.
Try changing to:
SELECT * FROM connections c JOIN information i ON i.member_id = c.member_id WHERE c.active = 1
Try this:
SELECT *
FROM information
LEFT OUTER JOIN connections
ON information.member_id = connections.member_id
WHERE connections.active = 1;
You're joining on the wrong tables. You said:
where member_id is my id and connection_id is my friends member_id on another table
Then, what you have to match is connections.connection_id with information.member_id. The simplest solution is:
select c.member_id, c.connection_id, c.active from connections c
join information i on c.connection_id = i.member_id
where c.active = 1 and c.member_id = #yourId
That's all :)
I'm new to database structure. I'm trying to create an app that allows users to like certain entries, but I want to be able to tie likes to users so that I can change the visuals before/after the like action.
I think from research that I should have an 'entries' and 'users' table and then have a 'likes' table that ties the two to each other.
The only thing I'm unsure of is, when getting and displaying the contents... how would I write the queries? If I query for all the entries I need, do I then go back and individually query each to see if it has a like tied to it for the current user? That seems like it might be a costly operation. Is there a more efficient way?
Hope that makes sense,
Thanks.
I think you have the right database design in mind. As far as queries are concerned, assume tables as such:
Users
ID | Name
1 | Bob
2 | Sally
Entries
ID | Name
1 | Red
2 | Blue
3 | Yellow
Likes
UserID | EntryID
1 | 1
1 | 2
2 | 2
2 | 3
So we can say Bob likes Red and Blue while Sally likes Blue and Yellow. So a query to retrieve all entries, plus an indicator of what Bob likes would be:
SELECT
e.ID,
e.Name,
l.UserID
FROM Entries e LEFT JOIN Likes l ON l.EntryID = e.ID
WHERE l.UserID = 1 -- Bob's User ID
ORDER BY e.Name
This would return
ID | Name | UserID
2 | Blue | 1
1 | Red | NULL
3 | Yellow | 1
The UserID column indicates if Bob likes the entry or not - a NULL is No and a value is Yes.
Assuming you have a table Entries with a column entity_id (and whatever else you store about the entity) and a second table UserLikes that contains the columns user_id and entity_id, you would do the following:
SELECT Entries.col1, Entries.col1 . . ., UserLikes.user_id
FROM Entries LEFT OUTER JOIN UserLikes ON
Entries.entity_id = UserLikes.entity_id
WHERE UserLikes.user_id = :user_id
AND Entity.col_whatever = :whatever
In this example, Entries.col1, Entries.col2 . . . is the list of columns you want to get back about the Entries. The :user_id is a parameter that contains the id of the user you're currently trying to display Entries for. And the last line is standing in for whatever limitations you want to put on the Entries are returned.
This query will give you a row for each Entry you searched for. You can check the value the returned column user_id. If it's NULL then it was not liked by the user, if it contains the user's id, it was liked by the user.
I think u can retrieve the entries and query the likes table at the same time to get if the current user likes the entry performing a stored procedure. So u can control the value of the set of data returned by the query for example returning one colum for the entry text and one boolean column to evaluates the current user likes... In this way you will at least one parameter for the stored procedure to indicate who is the current user
I hope this idea help u...