I have 2 tables in my MySQL database for users and groups. I need to relate users with groups and groups with the users. The only way that came my mind is having a group_ids col for users and user_ids col for groups. I have to do like this because I will show users' groups that they registered in their profile and I will show registered users in groups' users pages.
In this option I need to to store group ids for users like "2,5,14" and same in groups for registered user ids like "22,24,15 ...".
It sounds okey to me but parsing IDs on back-end from commas is not sounds "professional". And also I have concerns for the performance when there is huge amounts of users in a group.
I know this seems like a opinion based question but I have a question and I think it is not opinion based.
Is there a usage like this in "data science"? I mean, is this a common usage or am I missing something here because I really can't think something else.
You could create a new table called user_group wich stores the user_id and group_id as foreign key and primary key
The you can get all groups by user with
SELECT item1, item2...
FROM user
INNER JOIN user_group on user.user_id = user_group.user_id
INNER JOIN group on user_group.group_id = group.group_id
WHERE user.user_id = id;
Related
i am creating a restaurant review website. in my review table i have a foreign key called user_id and idk how to use it to display the username which is in the user table
my user table
my review table
so my question is how do i display the username from this? what mysql statement do i have to write. I am lost on what to do
Assuming you want to try and get the review text along with the user name from the corresponding user you can use a join to combine the info for example:
SELECT u.username, r.review_text
FROM reviews r
LEFT JOIN users u
ON (u.user_id = r.user_id)
I assumed the users table is called users and reviews table is called reviews but update those as necessary each is "aliased" as u and r respectively and then tables are joined
If the relationship between the two tables is mapped out correctly you should be able to run a query to fetch the name of each user. Try to avoid any N+1 query though
I have User objects stored in a Users table.
I have Permission objects stored in a Permissions table.
I have an MTM_UsersPermissions table that maps multiple User objects to multiple Permission objects. If User.id = 1 and Permission.id = 10, and this user has this permission, there is a record in MTM_UsersPermissions with ID_A = 1 and ID_B = 10.
I want to get all the Permissions associated with a given User, knowing the User ID.
I have a somewhat functional query:
SELECT Permissions.id, Permissions.Name, Permissions.Title, Permissions.Description, Permissions.OwnerURI FROM Permissions JOIN OTM_UsersPermissions ON OTM_UsersPermissions.ID_B = Permissions.id JOIN Users ON OTM_UsersPermissions.ID_A = :user_id;
(where user_id is the ID of the user)
This does seem to be retrieving only the permissions associated with each user. However, each permission is duplicated by the number of users present in the Users table. E.g., if the user has one permission assigned, but there are five users total, the correct permissions will be retrieved, but there will be five of each.
I don't have much experience with JOIN statements. I have tried to use this answer to get a working solution, but something's still lacking.
Clean way to get foreign key objects in PHP MySQL query
Using MySQL 5.5.
What am I missing?
ilmiont
You don't have to join Users table, your OTM_UsersPermissions table consists the user id already which will be used for filtering the result:
SELECT Permissions.id, Permissions.Name, Permissions.Title, Permissions.Description, Permissions.OwnerURI FROM Permissions JOIN OTM_UsersPermissions ON OTM_UsersPermissions.ID_B = Permissions.id
WHERE OTM_UsersPermissions.ID_A = :user_id;
I'm creating a website where the users can join certain groups. Now I need to maintain the set of users in each group and/or the set of groups that each user has joined. Since MySql doesn't support arrays, I cannot maintain say, an array of users in a group(as a field in the "groups" table) or an array of groups in a user(as a field in the "users" table). So how can I achieve this?
My current solution is to maintain a table of group-subscriptions which has fields for the userID and groupID. So when I need either of these two lists I can do,
SELECT USERID FROM SUBSCRIPTIONS WHERE GROUPID=3
or
SELECT GROUPID FROM SUBSCRIPTIONS WHERE USERID=4
This will get me the desired lists. Is this the most efficient/standard way to do this or is there a better way?
You wrote all right.
Normally there are 3 types of relations between records in relative databases:
One - one (e.g. user and profile linked via user.profile_id = profile.id)
One - many (user and messages linked via message.user_id = user.id)
Many - many
Your case is the last and it always works via a 3rd table.
For your case it can be users_subscriptions (user_id, subscription_id)
Example query to select all users with their subscriptions:
SELECT u.name, GROUP_CONCAT(s.name) as `subscriptions`
FROM users u
JOIN users_subscriptions us ON us.user_id = u.id
JOIN subscriptions s ON us.subscription_id = s.id
GROUP BY u.id
If I understand your question correctly, that is the standard way.
You've created a "pivot table" that sits between the user table and the groups table and it stores the relationships between the two. This is the way that many-to-many relationships are stored in relational databases. As you correctly stated, you can retrieve all members of a group or all groups for a member that way.
I have a rather special use case in front of me. There is to be an excel file with around a thousand entries (rows), each row represents something that the USER should pass judgment on.
Now, the entries are the same for everyone. The data that should be collected is
a) how many users like any given entry
b) what entries does any given user like
Since part of the app is already running and we have user accounts,
I thought of creating a table for each user (!) containing said excel information, adding a row for collecting the votes. I would create those tables by iteratin through the user list and creating tables like "userid_excelentries".
I don't think that's elegant. I would prefer to store the excel information only once in a table and only save the users' votes in the table "user".
The app is meant to display a table created form the excel table (I have the grid already done) and a row next to it with checkboxes. How do I structure this ? Temporary tables ? How do I store the information what each user has selected in the "user" table, since I don't know how many selections will be made a-priori ?
I had this crazy idea of actually handling the xls object through javascript, serializing it into a hash and storing that hash into a field in each user's row...but I have no clue if this is sane :o
We're facing a user count of exactly 272 - this is why I considered doing the "one table for each user" approach.
You can use 3 tables in your DB
users table
-----------
id
name
...
entries table
-------------
id
name
...
user_entries table
------------------
user_id
entry_id
user_response
To get all entries a certain user (i.e. Tom) likes you can do
select e.name
from entries e
join user_entries ue on ue.entry_id = e.id
join users u on ue.user_id = u.id
where u.name = 'tom'
and ue.user_response = 'like'
And to get the count of likes for each entry you can do
select e.name, count(ue.user_id) as likes
from entries e
join user_entries ue on ue.entry_id = e.id
where ue.user_response = 'like'
group by e.id, e.name
I am having a database design issue and i'm still pretty new to MySQL so I thought I would ask here. What would be the best way to get data for a chronological feed from multiple tables? For example a user does many things, they vote, comment, rate, ask questions. I save all this information in their respective tables "tblVote", "tblRate" etc, now the tricky part. a user can follow a user or many, so say you follow 3-4 people. Following allows you to see their interactions, voting, rating, commenting, asking questions etc in your feed (like facebook or something similar).
What would be the best way to get all the information from all 5 tables for every person they follow and then sort all of that chronologically? I Am assuming my current method (foreach follower grab all votes, comments, ratings etc and sort all would be terrible)
My working theory, so my working idea is to create a Interaction table, that has a column for the users id, the id of the other tables entry, and a type reference. so for example
User ID | InteractionID | Type
9 1232 Comment
10 80 Rating
9 572 Vote
Then you could just go ahead and grab all Interactions for each of the people they follow, sort that and then say grab the top 10? and query the individual databases to get the full info (time of comment, text of comment etc)
A many to many relationship exists between User and Follower. Since, Follower is also another user, this becomes a recursive many-to-many. When you decompose this relationship, you get a Association table or a gerund.
User_Follower {id, userid_fk, followerid_fk}
Both the userid_fk and followerid_fk are referencing to the User table.
Now, I am assuming you have a One-to-many relationship between User-tblRate, User-tblVote, User-tblPost etc.
So, you can write a join something like this:
select p.postTitle, p.postTag, ...,
c.commentId, c.commentData, ...
from (tblUser u INNER JOIN tblPost p
ON (p.userid = u.userid)) INNER JOIN tblComment c
ON (c.userid =
u.userid)
where u.userid in
(select userid_fk from user_follower where followerid_fk = 100)
orderby p.datetime_col ASC, c.datetime_col ASC
LIMIT 10;
100 is the user you want to get the information for.
The idea is that you just have one association table linking the User and Follower, then use simple joins to get the data for all the followees