I am new to database design so if this is an inefficient design, please let me know. This is my first post here and if you have any tips on how I could describe it better, I would appreciate it.
The situation is as follows:
Users register and are able to review other users
I have a table "Users"
I have a table "Reviews"
The review table has the following columns:
ReviewID
UserID (of the person who wrote the review)
Review: The actual review in text
Reviewed_User_ID: The UserID of the person who got reviewed
My question is: How would I go about creating a join that displays the columns: Users.First_name, Review.review, first_name of reviewed person
It will then read like: Name - wrote review about - Name. Instead of Name - wrote review about - UserID
The inner join like this:
SELECT users.first_name, review.review, review.reviewed_user_id
FROM users
INNER JOIN review ON users.user_id = review.user_ID
Will show me the reviewed_user_id but I would like to add the first_name of that person aswell. Is this even possible?
Many thanks in advance for any help or suggestions!
Please try to use something like that
SELECT users.first_name
, review.review
, review.reviewed_user_id
, reviewed_user.first_name
FROM users
INNER JOIN review ON users.user_id = review.user_ID
INNER JOIN users reviewed_user ON review.reviewed_user_id = reviewed_user.user_id
in this case we add other join to table users from table review by field reviewed_user_id with alias reviewed_user
Related
Newbie here.. Here's what I'm trying to do.
I have a Posts table with the following columns
id, userid, bodyText, date
and I have another table for users users.
When users submit a post, the user-id saves into the "posts" table under "userid". Well, I want to display that users information, such as name and picture, on the posts using the "userid" to get each users information so that their name and picture shows along with the post they submitted.
Sorry if I'm not being clear, english is not my first language and like I said, I'm new at this and still trying to learn.
I had it where when they submit the post, their name and picture also saves into the "posts" table but I want to change it because if the user updates their name or picture, it will still show the name and picture they had when they submitted the post. I want their name and picture to update on the posts if they update their information on the users table.
What you are asking about is a JOIN. In general the Join will look like
SELECT p.id. p.bodyText, p.date, u.name, u.picture FROM posts as p INNER JOIN users as u ON p.user_id = u.id where p.id = 123;
This will select the post with the ID 123 from the posts table and joins the users information from the users table based on the user_id columns value from the posts table.
In Syntax this could be something like
$sth = $dbh->prepare("SELECT p.id. p.bodyText, p.date, u.name, u.picture FROM posts as p INNER JOIN users as u ON p.user_id = u.id where p.id = ?");
$sth->execute(array(123));
$red = $sth->fetchAll();
Who can help me?
I have 4 tables posts, users, users details and comments.
Here is the strucutre:
posts
id
title
description
users
id
username
password
users_details
id
user_id
avatar
location
comments
id
post_id
user_id
parent
comment
posted
I have a query which i want to display comments on specific post.
This is what i written but avatar column it doesn't show any results. It seems i written it wrong on join or something.
SELECT comments.id as comment_id,
comments.user_id as user_id,
comments.post_id as post_id,
comments.parent as parent,
comments.comment as comment,
comments.posted as posted,
users_details.avatar as avatar,
users.username as username
FROM `comments`
LEFT JOIN users ON users.id = comments.user_id
LEFT JOIN users_details ON users_details.user_id = users.id
WHERE comments.post_id='60337'
ORDER BY posted ASC
Here is a screenshot of the table with results https://i.imgur.com/VQ8KwV1.png
I want to mention the avatar field it has a value for that user in users_details table so it should be displayed...
Thanks!
Two potential reasons I could tell causing this issue.
1. The users do not have an avatar.
Try: Select Avatar from Users_Details where User_Id in (2,9212) and make sure it returns some data.
2. The Primary/Foreign key being used for joining the tables is not matching
Run those queries below and ensure that they are returning the same users.
select * from users where id in (2,9212)
select * from users_details where user_id in (2,2912)
I am trying to display the profile name of a user's friend. I have a friends table (users table) and the myfriends table (friend table). Don't ask why the stupidly confusing names, it is what the assignment requires. Ill refer as the friendsID as user_id and myfriendsID as friends_ID just to eliminate confusion.
Now, so far I have got it to list the user_id and the friends associated with that ID.
I want it to be able to also display the friends names through a profile_name I have on the user_id table.
The SQL i have at the moment is:
SELECT friends.friend_id, myfriends.friend_id2, friends.profile_name
FROM friends
INNER JOIN myfriends
ON friends.friend_id = myfriends.friend_id1
WHERE friends.friend_id = '2'
Problem is, is that it lists the name of the USER_ID, not the friend_id. The profile names I am trying to obtain are also from the user_id table, but with their own unique user_id. If that makes sense?
Join back to friends/users again.
Inner join friends as f2
On f2.friend_id = myfriends.friend_id1
I'm trying to join 2 tables where I need to show only 3 columns from the second one where another column is used as a comparison.
For example:
Table one is called employee: it has a column called user_id and some other columns
Table two is called people: it has a column called user_id which included some of the employees user_ids
The columns I want to select are all from table people! (firstname, lastname, email)
I tried the following but something going wrong:
SELECT userid, firstname, lastname, email
FROM people
JOIN employee
WHERE people.userid = employee.userid;
I'm not sure what am I doing wrong, could you please help me correct it?
You can try this query:
SELECT
p.userid,
p.firstname,
p.lastname,
p.email
FROM
people as p,
employee as emp
WHERE
p.userid = emp.userid
Looking at your script, it looks like you'll run into ambiguous columns in at least your userid. You want to explicitly tell SQL where the column comes from like in your WHERE clause if there are columns sharing the same name between the two tables.
SELECT
userid, -- AMBIGUOUS
firstname,
lastname,
email
FROM people
JOIN employee
WHERE people.userid = employee.userid;
Example solution:
SELECT
people.userid,
people.firstname,
people.lastname,
people.email
FROM people
JOIN employee
WHERE people.userid = employee.userid;
For this issue you can use this query
let suppose that I have a users table where a user have zero to one profile picture
I need the user (Name,LastName,BirthDate) for users who have no profile picture
I can use this query
select *
from user c
where NOT EXISTS (
select 1
from photo p
where p.id = c.photo_id
)
in this where you can use any field between this two table
removing the not will result on the users who have a profile picture
hope this help you
you can search for SEMI JOIN and ANTI JOIN for more informations
i think this query will solve your problem
insert into table1 (clmn_1,clmn_2,clmn_3) SELECT clmn_1,clmn_2,clmn_3 FROM table2 where id = value
Here's one example, I have a Car, User, Member, and Dealer tables. At the moment I'm trying to get the name of a dealer who owns a car by matching their userids up
Select userid, name FROM `User` WHERE userid IN
(SELECT userid FROM 'Car' WHERE userid in
(SELECT userid FROM `Member` WHERE userid IN
(SELECT userid FROM `Dealer`)))
This does what I want but I can't help feel there's a better way of doing it? Currently the userid in Car is a FK of the userid in Dealer which is a FK of the userid in Member which is a FK of the userid in User which stores the name.
Can I go straight to getting all the userid's and names of dealers who's id is in the Car table, whilst making sure they're actually a Dealer?
Basically your schema is a downstream schema
Users -> Members -> Dealer -> Car
Good thing is you made all the possible keys that you need here.
So to selct anything in any table just go down stream from Users for example for the data you want
Select * from `USER` u
where
dealer.user_id = car.user_id and
member.user_id = dealer.user_id and
u.user_id = member.user_id
The reason i went upstream in matching records is because we want to make as few matching operations as possible. As you can see user table is supposed to contain the maximum records. So i match with car table and get all the user_id where there is a match in dealer. similarly i go from dealer to member and then to user. this means all the records of users will be matched with a lot fewer records that they would have been if i went from users to members to dealer to car.
But this is not fool proof solution. it will depend on your data. because it may be a case where one user may have multiple cars, then it would be better to go downstream.
Use JOIN instead of subqueries to fetch the data.
Try this:
SELECT U.userid, U.NAME
FROM `User` U
INNER JOIN Car C ON U.userid = C.userid
INNER JOIN Member M ON C.userid = M.userid
INNER JOIN Dealer D ON M.userid = D.userid;