I have these tables currently:
assignments(assignment_id, module_id, year, semester, title, number, weighting)
module(module_id, code, name, crn, course_title)
usermodule(usermodule_id, user_id, module_id)
users(user_id, title, first_name, last_name)
I was wondering if anyone could give me guidance on how to get the lecturer name, based on the module_id?
So far I've come up with:
SELECT `first_name` FROM `users` WHERE `assignments.module_id` = '$module_id';
I think I may have to do some form of JOIN query...
try this query
SELECT u.first_name FROM users u
LEFT JOIN usermodule um ON um.user_id = u.user_id
WHERE um.module_id = '$module_id';
How about
SELECT `first_name`
FROM `users` u INNER JOIN
`usermodule` um ON u.user_id = um.user_id
WHERE `um.module_id` = '$module_id';
Try rhis:
SELECT `first_name` FROM
`users` INNER JOIN `usermodule` ON `users.user_id`=`usermodule.user_id`
INNER JOIN `assignments` ON `usermodule.module_id` =`assignments.module_id`
WHERE `assignments.module_id` = '$module_id';
Just try below sql
SELECT `first_name` FROM `users` WHERE user_id = (select user_id from usermodule where module_id = '$module_id' limit 1))
I see poor structuring of your database.
You do not necessarily need a table usermodule to create relationships between the other tables.
If there is a relationship between a user and a module.
make use of a foreign key.
You could have a user_id in the module to link a user to a given module, then have 'module_id' in assignment to link a given assignment to a module, that way in the end, the user, module and assignment are related.
It will then be easy to use JOIN or simple select query
Related
I'm trying to make a query that returns the following:
All users such that:
-They are not an admin or owner account
-They have the same client_id as the project's client_id
-They are not already in the project_users table with entry project_users.project_id = 9
Here is my MySQL query:
SELECT `users`.`id` as id, `users`.`first_name` as first_name, `users`.`last_name` as last_name, `users`.`username` as username
FROM (`users`)
JOIN `projects` ON `projects`.`client_id` = `users`.`client_id` AND projects.id = 9
LEFT OUTER JOIN `project_users` ON `users`.`id` = `project_users`.`user_id`
WHERE `users`.`user_type` != 'Admin'
AND `users`.`user_type` != 'Owner'
For some reason, this query seems to return all non-super(not owner or admin) users with the same client_id as the project, but does NOT exclude those already in the project_users table (ie. the LEFT OUTER JOIN statement isn't working).
Can anyone tell me what is wrong with the query?
Thanks!
You need to add a filter to find the rows that don't match. Also, your query can be helped by using table aliases:
SELECT u.`id` as id, u.`first_name` as first_name, u.`last_name` as last_name, u.`username` as username
FROM `users` u JOIN
`projects` p
ON p.`client_id` = u.`client_id` AND p.id = 9 LEFT OUTER JOIN
`project_users` pu
ON u.`id` = pu.`user_id`
WHERE u.`user_type` not in ('Admin', 'Owner') and
pu.user_id is NULL;
I have three tables:
Table(attribute1, attribute2...);
---------------------------------
Users(iduser, username)
Link(idlink, title, userid)
Comment(idcomment, content, linkid, userid)
How to select:
Link title, with corresponding username and number of comments?
I'm currently doing like this:
Q1-Select links (SELECT * FROM `links`)
Q2-Extract usernames from previous query(Q1) - (SELECT username FROM `user` WHERE iduser=Q1.userid
Q3-Extract number of comments from Q1 by id (SELECT COUNT(*) as comments FROM `comment` WHERE linkid='Q1.idlink')
I believe we can do this in much more optimized way. I got idea how to get Link with corresponding username but I got stuck when I need to count comments.
SELECT iduser, username, Link.title, COUNT(idcomment)
FROM Users
LEFT JOIN Link ON (iduser = userid)
LEFT JOIN Comment ON (linkid = idlink)
GROUP BY iduser, idlink
Note that your Comment table is somewhat badly designed - the 'userid' field is not necessary, and can actually lead to situation where you've got a cross-linked record. e.g. a Comment belonging to user A might could be linked to a Link record belonging to user B.
It is good practice to get into the habit of putting the fields you want into both the SELECT and GROUP BY clauses, that way it won't come as such a shock when you have to use an RDBMS that insists on it.
SELECT
`l`.`idlink`,
`l`.`title`,
`u`.`username`,
COUNT(`c`,`idcomment`) AS `comment_count`
FROM `links` `l`
INNER JOIN `users` `u`
ON `l`.`userid` = `u`.`iduser`
LEFT JOIN `comments` `c`
ON `l`.`idlink` = `c`.`linkid`
GROUP BY
`l`.`idlink`,
`l`.`title`,
`u`.`username`
SELECT
l.idlink
, l.title
, l.userid
, u.iduser
, u.username
, c.idcomment
, c.content
FROM Link AS l
JOIN Users AS u ON u.iduser=l.userid
JOIN Comment AS c ON c.linkid=l.idlink
I have a user table, e.g.
userId
userName
and I have a message table, e.g.
messageId
messageToId
messageFromId
messageContent
I am trying to make a query to pull a message, but also get the user names from the user table based on the messageToId and messageFromId.
I have done this before with only 1 field between tables, e.g.
SELECT message.*, user.userName
FROM message, user
WHERE user.userId = message.messageToId
AND messageId = (whatever)
But I am having trouble with 2 links.
I want the result as follows:
messageId
messageToId
toUserName
messageFromId
fromUserName
messageContent
Any help would be much appreciated, or if someone had another way of attempting a private message system with PHP/MySQL.
You just have to use joins and different table aliases:
SELECT m.*, u1.userName AS toUserName, u2.username AS fromUserName
FROM message m INNER JOIN user u1 ON m.messageToId = u1.userId
INNER JOIN user u2 ON m.messageFromId = u2.userId
WHERE messageId = "XXX";
You need to use a join from to achieve this:
SELECT `m`.*,
`to`.`userName` AS `to`,
`from`.`userName` AS `from`,
FROM `message` `m`
JOIN `user` `to` ON `m`.`messageToId` = `to`.`userId`
JOIN `user` `from` ON `m`.`messageFromId` = `from`.`userId`
WHERE `m`.`messageId` = 1
So you join against the user table twice to get both users for a particular message. To do this you need to use table aliases as I have done with to and from so that you distinguish between them.
I have also used a field alias to get their usernames separately eg:
`to`.`username` AS `from`
Will this work?
SELECT b.userName AS author, c.userName AS reciever, a.messageId, a.messageContent FROM message a JOIN user b ON a.messageFromId = b.userId JOIN user c ON a.messageToId = c.userId
Im making a codeigniter webapp where users can add each other in a contactslist.
The table looks like this:
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_1` int(11) NOT NULL,
`user_2` int(11) NOT NULL,
`accepted` tinyint(2) NOT NULL,
PRIMARY KEY (`id`)
The userid for the user that makes the request to add the contact is always stored in user_1 column. The other users userid is stored in user_2. user_2 then has to accept the request and the 'accepted' column gets updated to 1.
I want to list all contacts that are accepted (WHERE accepted = 1) in a html table, and the contact requests (accepted = 0) in another.
My question is: How can i make a mysql query that selects all the rows and just get the userid from the contact? Its a problem since they can be in either user_1 or user_2 (Depending on if they requested or accepted).
Should i change the db table in some way to achieve this. Or could i make a query (active rcords preferably) that accomplish this?
Any help is appreciated
Thanks in advance
George
Update:
So the final query looks like this:
SELECT DISTINCT users.id, users.username, contacts.accepted
FROM users
LEFT JOIN contacts ON users.id = contacts.user_1
WHERE contacts.user_2 = ' . $this->session->userdata('user_id') . '
UNION DISTINCT
SELECT DISTINCT users.id, users.username, contacts.accepted
FROM users
LEFT JOIN contacts ON users.id = contacts.user_2
WHERE user_1 = ' . $this->session->userdata('user_id')
And works exactly as i described :)
Use a UNION query. See the documentation.
SELECT DISTINCT user_1 userid FROM user WHERE accepted = 1
UNION DISTINCT
SELECT DISTINCT user_2 userid FROM user WHERE accepted = 1
About the join, you'd use something like below for each part of the UNION
SELECT DISTINCT users.userid, users.username, contacts.accepted
FROM users
LEFT JOIN contacts ON users.userid = contacts.user_1
WHERE contacts.user_2 = ?
Shouldn't the contactlist be owned by the user?
create table Contactlist (
OwnerID int, -- ID of the owning User
ContactID int, -- ID of the contact User
Accepted bool)
-- With composite primary key on OwnerID, ContactID
This way the query would be
select * from User
left outer join Contactlist on User.ID = Contactlist.OwnerID
left outer join User as Contact on Contactlist.ContactID = Contact.ID
Sorry... Overthunk the select ;)
select * from Contactlist
inner join User on Contactlist.ContactID = User.ID
where Contactlist.OwnerID = <the querying users ID>
(MSSQL syntax)
You can use queries but it will create problems later on I guess as I have also faced this problem before. You can insert new entries in the same table when a user accepts the request and mark the new record as accepted but this time the user_1 becomes user_2 and vice versa.
Alias with joins is waht I think you are asking.
Something like.
Select c.id, uRequest.UserName, uRequested.UserName From Contacts c
inner join Users As uRequest On c.User_1 = uRequest.id
inner join Users As uRequested On c.User_2 = URequested.id
Where accepted = 1
will give you all contacts where the request has been accepted.
Let's say I have two tables, users and notes. Let's say the schemas look like this:
users
id, name, field2, field3
notes
id, user_id, subject, heading, body, timestamp
What I want to do is select every user, and the LATEST (just 1) note posted by each user based on the timestamp to show in an overview report.
How would I go about doing this? Please note that the DB is MySQL.
Thanks!
select users.name, notes.subject, notes.heading, notes.body
from users, notes
where users.id = notes.user_id
and notes.timestamp = (select max(timestamp) from notes where user_id = users.id)
select u.id, u.name, n.id as note_id, n.subject, n.heading, n.body, n.timestamp
from users u
left outer join (
select user_id, max(timestamp) as timestamp
from notes
group by user_id
) nm
left outer join notes n on nm.user_id = n.user_id and nm.timestamp = n.timestamp
Note that this could potentially return duplicates if the user has two notes with the exact same timestamp. I have assumed this is not the case.
SELECT *
FROM `users`
LEFT JOIN `notes`
ON `user_id` = `users`.`id`
WHERE `notes`.`timestamp` = (
SELECT MAX(`timestamp`)
FROM `notes` AS `notes_1`
WHERE `notes_1`.`user_id` = `notes`.`user_id`
)