I have some trouble setting upp a database. Not any coding problems but can't figure it out how to structure it.
The idea is that people will sign up on the site, and with SQL they will be in the table USER.
But the users will also availbaile to have a collection of handmade products so other users will see and rate their handmade products and see a lot of others information. So instead of having a table for each user, is there any easier way?
The product should only be "tied" to one user. No user would be able to have same identical product.
Like how does facebook work? I dont think every user have their one table for the information on use? The products could be like a picture. So every album dosen't have a table? Right?
Having separate table for each user is intolerable and completely wrong according to relational database model!
The goal you want to achieve is actually quite a basic thing in DB structuring, try reading some tutorials in that topic.
With a table USER and PRODUCT and properly set key fields, you'll be able to get the right form.
USER: user_id, << user details >>
PRODUCT: product_id, user_id, rank, << other product details >>
So with a query below, you'll be able to get all products of your users.
SELECT *
FROM db.user u
(LEFT) JOIN db.product p
ON u.user_id = p.user_id
The usual SQL approach is to create a table for the users and a table for the products. The products table should have a row "user" which contains the user id (or something else identifying the user). You might want to assign an ID to each user (e.g. autoincrement int) and use it.
You can then select all products of a given user:
SELECT * FROM products WHERE user = 723;
Or you might want to find the name of a user who made a product:
SELECT name FROM users WHERE rowid = (SELECT user FROM products WHERE product_name = 'Kitchen Chair');
By the way, I'd always use lowercase names for tables and rows in SQL.
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'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 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
I am developing web application where I have to implement 'Likes' system as facebook has. Application will have a few categories of products that customer can 'like'. So I have started to create database, but I stuck on one obstacle. As I understand there are two ways of doing this:
First. Create one database table with fields of "id, user_id, item_category, item_id". When user click 'like' button information will be saved in this table with various categories of products (item_category).
Second. Create several tables for certain categories of item. For instance, "tbl_item_category_1, tbl_item_category_2, tbl_item_category_3" with fields of "user_id, item_id".
Would be great to get more insight about best practices of this kind database structures. Which works faster? and more logical/practical? I will use only several categories of items.
I would go with the first version with a table structure similar to this:
User Table: PK id
id
username
Category Table: PK id
id
categoryname
Like Table: PK both user_id and catgory_id
user_id
category_id
Here is a SQL Fiddle with demo of table structure with two sample queries to give the Total Likes by user and Total Likes by category
The second one - creating multiple tables is a terrible idea. If you have 50-100 categories trying to query those tables would be horrible. It would become completely unmanageable.
If you have multiple tables trying to get a the total likes would be:
Select count(*)
from category_1
JOIN category_2
ON userid = userid
join category_3
ON userid = userid
join .....
Use one table, no question.
The first method is the correct one. Never make multiple tables for item categories, it makes maintaining your code a nightmare, and makes queries ugly.
In fact, the general rule is that anything that is dynamic (i.e. it changes) should not be stored as a set of static objects (e.g. tables). If you think you might add a new type of 'something' later on, then you need a 'something' types table.
For example, imagine trying to get a count of how many items a user has liked. With the first method, you can just do SELECT COUNT(*) FROM likes WHERE user_id = 123, but in the second method you'd need to do a JOIN or UNION, which is bad for performance and bad for maintainability.
The first method is the correct one. Because you dont know how many categories you will be having and it is very difficult to get the data.
I want to create some kind of 'activity feed'. For example, There are total 1000 users in database, of which there are 100 people in contact list of user X, who is concerned with those 100 users only, and want that if any of them posts a note (in general, takes an action), he wants to get that update on my page. For this purpose, do i need to make a database table, like:
id user_id note_id
In this table, there will be users which are not concerned to user X, so I will make some query like,
select user_id from activity_table which exists in contact list of user X
Is my approach correct regarding this matter (for example database table design and query)?
Is there any better approach?
If I understand you correctly I think you need a relation table where you will store user_ids of the user that is being concerned and of the user that concerns.