Well I'm trying for last 5 days to create simple register, confirm, login PHP script, which is for assignment at UNI, but thing which I'm trying for last 5 days and it's not working is adding friends into friend list. Kid a like Facebook but much much simpler, it's for Android game we got as group assignment.
I have one TABLE users where I have fields ID, username, password, email, friends.
Into field friends I would like to save multiple values as ID's of your friends. To retrieve in game some of user information.
This db and tables are on MySQL and INSERT or UPDATE are not working for me, INSERT is creating new record and can't insert only to one column of existing record and UPDATE can't just insert value but will delete old one and insert new one in.
Seeing as this is a many-to-many relation (if I'm correct) so it'd be smart to create a seperate table that records this.
Table: Friends
userID
userID2 (or friendID)
Which you can fill.
For more info: http://www.singingeels.com/Articles/Understanding_SQL_Many_to_Many_Relationships.aspx
Normally you would add a freinds table with the fields:
user_id
friend_id
where both fields are references to the user tables id field.
If you - for some reason - need it to be a field in user table serialize the id values and save them there.
ATTENTION: you won't be able to easily join the tables and there is no automated possibility to keep integrity. If a user is deleted none of the references to this user in friends field will be deleted. This would all be possibile with the secondary friends table and foreign keys.
What you've described here is a many-to-many relationship between people and their friends. The canonical way do implement this in a relational database is to use a pivot table in which each row represents a "friendship" between two people. You'd have two fields to hold the IDs:
users table:
id, name, email, etc.
friendships table:
user_id_1, user_id_2
Then if user 1 is friends with user 2 and user 3, you'd have records (1,2) and (1,3) in the friendships table. You can treat these as reciprocal relationships if you like, or you can require a (2,1) record to denote that user 2 is also friends with user 1.
Related
it's late, my child cried all dayand I'm expected to pull this off by the next 3 hours.
I have a 3 MySQL tables "entities", "users", "priviledges" (all have their id as key).
The table "priviledges" is having these columns: id(PRIMARY KEY), user_id, entity_id, priviledge
The thing is that when...
I grant the highest priviledge(3) to a user the system should create new table entries for all remaining entities
(once you become "admin" for one entity, you should be "admin" for all entities; if you should have priviledge(2) for some entity already, it should be changed to 3).
I cannot alter the SQL structure and I'm using PHP with PDO. I tried, but I always end up with duplicate entries in "priviledges" as I'm not able to utilise INSERT IGNORE (yep, still SQL noob).
Right now I just select all users with priviledges.priviledge(3), then I select all DISTINCT entities.id and dump them into PHP arrays and then I loop foreach through every "user" and "entity". So instead of sending 1 query, I'm ending with USERSxENTITIES and rightnow its over 500 queries.
Will there be a merciful soul to help me?
First it seems from your data structure that (user_id, entity_id) is meant to be unique.
Because of your "no table schema changes" criteria (otherwise I'd drop id (assumed to be an auto_increment) and add this as the primary key), so instead, create a unique index:
CREATE UNIQUE INDEX uniq_u_e ON priviledges (user_id, entity_id)
You probably have duplicate already so search existing questions for deleting duplicates and then add this index.
I assume you have another table of entities.
To create an admin (3) user on all entities that has an id as its entity primary key.
INSERT INTO priviledges( user_id, entity_id, priviledge)
SELECT 42 as user_id, id, 3
FROM entities
ON DUPLICATE KEY
UPDATE priviledge = 3
So this ensure that the user 42 has admin(3) access on all entities.
I am developing a reservation system for my school project. It is based on PHP and MYSQL.
The system allows a user to register. After successful login, the users can make a reservation which is stored in the following table in phpmyadmin.
User Table
When a user registers, he gets a user_id. When a user makes a reservation, the data is inserted into the table against the same user_id. But when the user tries to make another reservation, there is no way to store the information of the next reservation.
The question is how do I allow the user to make several reservations?
The user_id is my primary key so I understand it is not possible to create multiple records against one primary key.
Do I have to create a new reservation table and link it to user_id through a Foreign key relationship>? But if my reservation table has a primary key, then several records cannot be inserted against one primary key.
Somehow, each reservation must be linked the unique user_id so that the user can check all the bookings under his name.
Each reservation also needs a unique ID which can be used to cancel/update the reservation.
I believe it must be a basic MySQL question. Something like creating a new reservation table and connecting it with user_ID but I am unable to think of a concrete solution.
Your help is very much appreciated.
Thank You.
Make table users
then at least 2 fields id, name
then make table reservations and its One-To-Many relation so you need to put foreign key in reservation(many side)
reservation
id, name, user_id
then to get reservations from user 1 use select with join
SELECT * FROM reservations r JOIN user u ON r.user_id = u.id WHERE u.id = 1
Now I have 2 tables: demo(detailed information about users) and users(login and password), then I create a junction table(ID, demo_ID and user_ID).
The system working like this:
User register
User login
User fill form where he gave a detailed information
And I want to fill junction table automatically with user_ID and demo_ID where user_ID will LOGGED USER and demo_ID the information of exactly this user.
How can I do this? Please help me =)
You can use query like -
INSERT INTO rel_users_demo (demo_ID,users_ID) SELECT demo.ID, users.ID join on demo.EMail = users.email
You have not mentioned which column you have in common(foreign key) between demo and users. you can keep your column at place of xx and yy.
Just a really simple question. In my SQL database I have a column named "friend_count" in table "users" to record all friends the logged in user has. This works with UserID numbers and I am trying to figure out how to record them all. Here's my example:
USER #29 becomes friends with USER #422
In the user database under USER #29's info in the column "friend_count" there will then be the number "422", if he then becomes friends with USER #500, it will show "422, 500" and so on... If he deletes one, that particular number is removed from the box. The script will then search these numbers through the user database to show a list of the people you are friends with.
How can I do this? Any ideas? Thanks!
Any time you have a delimited list of values in a column it's almost always a sign that the data model is incorrect. (Actually, I can't think of an exception to this, but I'll stick with "almost always" just to be safe.)
In this case you have two types of entities:
User
Friendship
A friendship, though not a physical object, is a conceptual entity in and of itself. It connects two users and can add more information related to the friendship itself but not necessarily to the two users.
So you might have tables like this:
User
--------
ID
Name
etc.
Friendship
--------
ID
OriginatingUser
AcceptingUser
BecameFriendsOn
etc.
So OriginatingUser might be the user who sent the friend request, and AcceptingUser might be the user who accepted it. BecameFriendsOn is the date it was accepted. You'd probably want to have statuses and other dates to keep track of pending requests, denied requests, etc. But all of this information is related to the friendship, not necessarily to the users.
The concept you're looking to understand here is called a Foreign Key. The OriginatingUser and AcceptingUser columns are the same data type as the ID column on the User table. You would create the Friendship table such that those columns are foreign keys to the User table, this enforces the integrity of the data so that you can't create a Friendship record without two valid and existing User records.
Then to get the list of friends, you'd join the tables in a query. Perhaps something like this:
SELECT
User.Name
FROM
Friendship
INNER JOIN User ON Friendship.AcceptingUser = User.ID
WHERE
Friendship.OriginatingUser = ?
When supplied with the ID of the originating user, this would get all of the names of users to whom that user sent a friend request. You can further build on the query to also get users who sent this same user a friend request, and so on. By making use of the key foreign key relationships between tables which represent different types of entities in the system, you can construct very robust queries to view that data in lots of different ways.
You are describing a relationship between two entities so you can create a table to store the details of that relationship.
Suppose that you have your user table with a userid column and other columns. You can then create a friends table with two columns that are both foreign keys to the user table.
friends = (user, friend)
Thus, for each friend that user #29 gets you need to add a row into the friends table. For example:
USER
ID NAME ...
29 Sam
30 Henry
32 Jane
Friends
user friend
29 30
29 32
Sam is friends with both Jane and Henry but Jane and Henry are not friends.
I would create a table "friendship" with two cols "user" and "friend", then you start adding pairs of user/friend ids
users table:
id, username, whatever else
friends table:
relationship_id, user_id, user_friend_id
example query to get a list of IDs that belong to the users friends:
SELECT f.user_friend_id FROM users u
LEFT JOIN friends f ON f.user_id = u.id
WHERE u.id = {$user_id}
A very simple approach, assuming that if UserA becomes friends with UserB , then UserB also becomes friends with UserA.
Usually, Comma Separated Lists are not recommended, as they will become a pain when the list is very large. A simpler approach will be, make a table friends with columns user_id and friend_id Where user_id and friend_id are the respective UserIDs .
Now when you want to add a friend to someone's list, use the following :
INSERT INTO users (user_id,friend_id) VALUES(UserA,UserB),(UserB,UserA)
Now when you execute the above query, you will have 2 new rows in your friends table :
user_id friend_id
UserA UserB
UserB UserA
When you want to get the list of a user's friends, use :
SELECT friend_id FROM friends WHERE user_id=(Your user's ID)
This will return a row one by one, and hence will give you all the IDs of friends of a particular user.
Now when you want to delete a friend, use :
DELETE FROM friends WHERE (user_id,friend_id) IN ((user_id,friend_id),(friend_id,user_id))
This removes both the rows from the table, which means that the relationship between UserA and UserB is deleted, and neither of them is friend of each other.
Okay so im new to databases, and have created a site with a users table, and i also hace a list table, where suers can insert list items, however when they log in everyones list is appearing, how can i link the user table to the lists table, is it creating the same field in each one and using a foreign key? Sorry I am very new to this. Appreciate any help
I think you can just use user_id on both tables to fix this. Let me give an example:
Table A (user_id, username, password)
Table B (list_item_id, user_id , any_other_attribute)
When you design your tables like this a simple sql call will do what you need like:
SELECT 'list_item_id','any_other_attribute' FROM Table B Where user_id=$user_id
Where $user_id is the user_id of the one's who loginned your system.
Also by your question, i suggest you to read about these : 'sessions' , 'sql queries' , 'generating sql query results' on your choice of programming language.
It calls MANY MANY relationnship. There mus be 1 table with fields user_id and field_id that will join this 2 tables