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'
Related
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.
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
I have two tables, one stores the users, the other stores the users' email addresses.
table users: (userId, username, etc)
table userEmail: (emailId, userId, email)
I would like to do a query that allows me to fetch the latest email address along with the user record.
I'm basically looking for a query that says
FIRST ORDER BY userEmail.emailId DESC
THEN GROUP BY userEmail.userId
This can be done with:
SELECT
users.userId
, users.username
, (
SELECT
userEmail.email
FROM userEmail
WHERE userEmail.userId = users.userId
ORDER BY userEmail.emailId DESC
LIMIT 1
) AS email
FROM users
ORDER BY users.username;
But this does a subquery for every row and is very inefficient. (It is faster to do 2 separate queries and 'join' them together in my program logic).
The intuitive query to write for what I want would be:
SELECT
users.userId
, users.username
, userEmail.email
FROM users
LEFT JOIN userEmail USING(userId)
GROUP BY users.userId
ORDER BY
userEmail.emailId
, users.username;
But, this does not function as I would like. (The GROUP BY is performed before the sorting, so the ORDER BY userEmail.emailId has nothing to do).
So my question is:
Is it possible to write the first query without making use of the subqueries?
I've searched and read the other questions on stackoverflow, but none seems to answer the question about this query pattern.
But this does a subquery for every row and is very inefficient
Firstly, do you have a query plan / timings that demonstrate this? The way you've done it (with the subselect) is pretty much the 'intuitive' way to do it. Many DBMS (though I'm not sure about MySQL) have optimisations for this case, and will have a way to execute the query only once.
Alternatively, you should be able to create a subtable with ONLY (user id, latest email id) tuples and JOIN onto that:
SELECT
users.userId
, users.username
, userEmail.email
FROM users
INNER JOIN
(SELECT userId, MAX(emailId) AS latestEmailId
FROM userEmail GROUP BY userId)
AS latestEmails
ON (users.userId = latestEmails.userId)
INNER JOIN userEmail ON
(latestEmails.latestEmailId = userEmail.emailId)
ORDER BY users.username;
If this is a query you do often, I recommend optimizing your tables to handle this.
I suggest adding an emailId column to the users table. When a user changes their email address, or sets an older email address as the primary email address, update the user's row in the users table to indicate the current emailId
Once you modify your code to do this update, you can go back and update your older data to set emailId for all users.
Alternatively, you can add an email column to the users table, so you don't have to do a join to get a user's current email address.
I am using SQL Server 2005. I have three tables - Users, Groups, and GroupUsers. GroupUsers contains the two PKs for a many-to-many relationship.
I have a view to get all the user information for a group as follows:
SELECT * FROM GroupUsers JOIN Users ON GroupUsers.UserID = Users.UserId
I want to create the inverse of this view - I want a list of all of the users NOT attached to a specific group. The following query would accomplish this:
SELECT * FROM Users WHERE UserID NOT IN
(SELECT UserID FROM GroupUsers WHERE GroupID=#GroupID)
However I don't want to have to specify the group, I want to know how to turn this into a view that joins the GroupID and then the UsersID and all the user info, but only for non-attached users.
I'm not sure how to do this, maybe something with the EXCEPT operator?
UPDATE:
I think this is my solution, unless someone comes up with something better:
SELECT
G.GroupId,
U.*
FROM
Groups G
CROSS JOIN
Users U
WHERE
U.UserId NOT IN
(
SELECT
UserId
FROM
GroupUsers
WHERE
GroupId=G.GroupId
)
You can use a left outer join to grab all of the users, then, blow away any user where there's a group attached. The following query will give you just the list of users where there's no group to be had:
select
u.*
from
users u
left outer join groupusers g on
u.userid = g.userid
where
g.userid is null
If you want to find all users not in a particular group:
select
u.*
from
users u
left outer join groupusers g on
u.userid = g.userid
and g.groupid = #GroupID
where
g.userid is null
This will only exclude the users in that particular group. Every other user will be returned. This is because the groupid condition was done in the join clause, which limits the rows joined, not returned, which is what the where clause does.
If I understand it correctly, you will have to do a cartersian result of users & groups and reduce the result derived from GroupUsers.
That will give you records of users which do not have any groups attached to it.
I apologize if I didn't understand the question correctly.
EDIT: Cartesian result will give you users * groups. You will have to subtract GroupUsers from it. I am sorry, I do not have SQL ready for it & can't try it out at this point.
I couldn't figure out how to get previous version to work via active record, got some of the way there but had to write an SQL in statement. I believe this also accomplishes the same thing.
SELECT * FROM Users WHERE UserID NOT IN
(SELECT U.UserID FROM GroupUsers AS G, Users as U WHERE G.UserID <> U.UserID)
Couldn't test however this query in rails worked just fine:
# Gets Pre-Clients. Has client information but no project attached
Contact.joins(:client).includes(:projects => :primary_contact).
where("contacts.id NOT IN (select contacts.id from contacts,
projects where projects.primary_contact_id = contacts.id)")
Thanks for the post got me 90% of the way there.