I have two tables, Users and Relationships tables. Users table has following columns:
id, name,password,username,email,avatar,followersCount,followingCount,tweetCount.
And the Relationships table has the following columns:
id, followingId, followerId
How should I go about creating a SQL query to extract a user with a specific Id and find id's from Relationships that user is following? So in other words find people that user follows
I've come this far so long
SELECT *
FROM public."Users" JOIN
public."Relationships"
ON (public."Users".id = public."Relationships".id)
If I understand correctly, you want:
SELECT u.*
FROM public."Relationships" r JOIN
public."Users" u
ON u.id = r.followerId
WHERE r.followingId = ?;
? is a parameter placeholder for the user you care about. This returns all the followers of that user.
Do you mean this query
SELECT public."Users".*
FROM public."Users"
JOIN public."Relationships"
ON public."Users".id = public."Relationships".followingId
AND public."Relationships".followerId = a user ID
I am not really clear about followerId and followingId mean but you can change them in the query if it is not what you want.
Related
This is task table:
This is user table:
I want to select user tasks.
I would give from backend ("given_to_user) id.
But The thing is I want that SELECTED data would have usernames instead of Id which is (created_by_user and given_to_user).
SELECTED table would look like this.
Example:
How to achieve what I want?
Or maybe I designed poorly my tables that It is difficult to select data I need? :)
task table has to id values that are foreign keys to user table.
I tried many thinks but couldn't get desired result.
You did not design poorly the tables.
In fact this is common practice to store the ids that reference columns in other tables. You just need to learn to implement joins:
SELECT
task.id, task.title, task.information, user.usename AS created_by, user2.usename AS given_to
FROM
(task INNER JOIN user ON task.created_by_user = user.id)
INNER JOIN user AS user2 ON task.created_by_user = user2.id;
Do you just want two joins?
select t.*, uc.username as created_by_username,
ug.username as given_to_username
from task t left join
users uc
on t.created_by_user = uc.id left join
users ug
on t.given_to_user = ug.id;
This uses left join in case one of the user ids is missing.
Sorry about this dreadful title. Imagine tables like this: http://sqlfiddle.com/#!9/48d921/1
Here, we run a query for all users with the name "Bob", but we are also interested in all users in the same postcode as "Bob" and also all users of the same "type" as Bob.
You can see I joined the same tables twice to achieve this. The trouble with it is it doesn't scale; the more criteria I want to "explore" the more times I have to join the same tables, making the select statement more cumbersome.
So:
What's the best way to do this?
Does this type of query have a name?
The answer updated
SELECT
FROM user
where u.name="Bob"
OR (u.postcode in (SELECT a.postcode
FROM USER u
JOIN ADDRESS a on a.user=u.id
WHERE u.name="Bob")
)
OR (u.type in (SELECT ut.type
FROM USER u
JOIN USER_TYPE ut1 on u.id=ut1.user
WHERE u.name="Bob")
)
So you scan users table just once for each record checking the linking criteria
The database is Oracle XE .
Let me explain the scenario first ,
Two tables Movie and UserInfo are in a relationship many to many using the junction table Rating.
Rating ( MovieID (FK) , UserName(FK) , Rating)
MovieID and UserName are both respectively the primary keys in the respected tables.
What I am trying to do is make a select statement to select the MovieNames from the Movie table where UserName is not equal to the given input. As the MoveID was the FK, but I need to retrieve MovieName if the movie is not already been rated by the GIVEN user, so I guess I may need to make a rather complex joining operation - which I can't figure out or maybe joining two or more different query using where.
Thanks in advance and please if possible give an explanation about the solution.
This seems like a classic usecase for the not exists operator:
SELECT *
FROM movie m
WHERE NOT EXISTS (SELECT *
FROM rating r
WHERE r.movideid = m.moveid AND
r.username = 'given username here')
Sorry if that title is a bit convoluted... I'm spoiled by an ORM usually and my raw SQL skills are really poor, apparently.
I'm writing an application that links to a vBulletin forum. Users authenticate with their forum username, and the query for that is simple (selecting by username from the users table). The next half of it is more complex. There's also a subscriptions table that has a timestamp in it, but the primary key for these is a user id, not a username.
This is what I've worked out so far:
SELECT
forum.user.userid,
forum.user.usergroupid,
forum.user.password,
forum.user.salt,
forum.user.pmunread,
forum.subscriptionlog.expirydate
FROM
forum.user
JOIN forum.subscriptionlog
WHERE
forum.user.username LIKE 'SomeUSER'
Unfortunately this returns the entirety of the subscriptionlog table, which makes sense because there's no username field in it. Is it possible to grab the subscriptionlog row using the userid I get from forum.user.userid, or does this need to be split into two queries?
Thanks!
The issue is that you are blindly joining the two tables. You need to specify what column they are related by.
I think you want something like:
SELECT * FROM user u
INNER JOIN subscriptionlog sl ON u.id = sl.userid
WHERE u.username LIKE 'SomeUSER'
select * from user u JOIN subscriptions s ON u.id = s.id where u.username = 'someuser'
The bit in bold is what you want to add, it combines the 2 tables into one that you return results from.
try this
SELECT
forum.user.userid,
forum.user.usergroupid,
forum.user.password,
forum.user.salt,
forum.user.pmunread,
forum.subscriptionlog.expirydate
FROM
forum.user
INNER JOIN forum.subscriptionlog
ON forum.subscriptionlog.userid = forum.user.userid
WHERE
forum.user.username LIKE 'SomeUSER'
I'm building this bartering-type function in this site using PHP/MySQL and I'm trying to create a query that responds with the following fields:
owner's username, title, offerer's username, offerer's item
Basically I have three tables here with the following fields:
users
user_id, username, email
items_available
item_number, owner_id (foreign key that links to user_id), title
offers_open
trade_id, offerers_id (fk of user_id), offerers_item(fk with item_number), receivers_id (fk from user_id)
How do I do this? I've seen some references to many-to-many SQL queries but they don't seem to particularly fit what I'm looking for (for example, the offerers_id and the owner_ids refer to different users_id in the Users table, but how do I make them distinguishable in the sql query?)
If I understand correctly, this is what you are looking for:
SELECT owner.username, oferrers.username, ia.title
FROM offers_open o
INNER JOIN users AS offerers
ON o.offerers_id = offerers.user_id
INNER JOIN items_available AS ia
ON o.offerers_item= ia.item_number
INNER JOIN users AS owner
ON ia.owner_id = owner.user_id
I don't see a title on the users table, so didn't include one.
I'm not sure exactly what output you want, but since your users table will appear twice in the query, they need to be aliased like so:
SELECT offerer.username AS offerer_username, title, receiver.username AS receiver_username
FROM users AS owner
JOIN items_available ON owner_id = owner.user_id
JOIN offers_open ON offerers_item = item_number
JOIN users AS receiver ON receivers_id
Again, don't know if that's what you want, but hope you get the idea.
It sounds as you need an alias of the users table.
Something like?
select
u.*, ia.*, oo.*,u2.*
from
users as u,
items_available as ia,
offers_open as oo,
users as u2
where
u.user_id = ia_user_id and
oo.user_id = u2.user_id and
oo.item_id = ia.item_id