So I have two tables that i'm working with.
Users which consists of:
ID, NAME, CITY
Follow which consists of:
User(id), Follow(id)
I am trying to write a query that returns to me a table of the name of the user, the name of the follower's name and the followers city. I have this query written which returns the correct information, but prints it out 8 times for each row and I have no idea why.
Here is a link to my code
https://www.db-fiddle.com/f/aDPgZFknC1ybteWM6hwoFJ/3
FROM
(SELECT user.name
from follow, user
where follow.user = user.id) as NAME,
(Select user.name
from follow, user
where follow.follow = user.id) as FOLLOWER,
(select city
from user
right join follow
on user.id = follow.follow) AS CITY;
When joining tables it would be better to use the JOIN syntax. You can use as your base the follow table and transform it through the use of JOIN to display the information that you need. On the following example, you join follow with the user table two times to get the user and follower information.
SELECT U.name, U2.name, U2.city
FROM follow AS f
JOIN user AS U
ON f.user=U.id
JOIN user AS U2
ON f.follow=U2.id;
Related
I need to find out how to pull user names into a VIEW from a different table. I have 3 tables, User, Lead, and Lead_detail. In the users table there is an ID field which is stored in the Created_By field in the Lead table. In the Lead table I have an ID field that is stored in the Lead_detail Lead_ID field.
I have created a VIEW to the Lead_detail table which pulls all the info I need but I have found that I don't have the users name in that VIEW so I need to ALTER my view to add in the users names per lead but I am having trouble with the statement.
Before altering the VIEW I wanted to try a SELECT statement to see if I get any data,
SELECT * FROM Lead_detail
JOIN Lead
ON Lead_detail.lead_id = Lead.id
WHERE Lead.Created_by = Users.ID
But this didn't work. What would be a correct statement so that I can pull the users names into the Lead VIEW?
I think you missed a join to the Users table:
SELECT
*
FROM
Lead_detail
INNER JOIN Lead
ON Lead_detail.lead_id = Lead.id
INNER JOIN Users
ON Lead.Created_by = Users.ID
Suppose I have 3 different tables relationships as following
1st is tbl_users(id,gender,name)
2nd is tbl_feeds(id,user_id,feed_value)
3rd is tbl_favs(id,user_id,feed_id)
where id is primary key for every table.
Now suppose I want to get data where those feeds should come which is uploaded by Gender=Male users with one field in every row that should say either the user who is calling this query marked that particular feed as favourite or not.
So final data of result should be like following :
where lets say the person who is calling this query have user_id=2 then is_favourite column should contain 1 if that user marked favourite that particular feed otherwise is_favourite should contain 0.
user_id feed_id feed_value is_favourite gender
1 2 xyz 1 M
2 3 abc 0 M
3 4 mno 0 M
I hope you getting my question , I m able to get feeds as per gender but problem is I m facing problem to get is_favourite flag as per particular user for every feed entry.
I hope some one have these problem before and I can get help from those for sure.
I would be so thankful if some one can resolve my this issue.
Thanks
Something like this should work:
SELECT
u.id AS user_id.
fe.id AS feed_id,
fe.feed_value,
IFNULL(fa.is_favourite, 0),
u.gender
FROM
tbl_users u
JOIN
tbl_feeds fe ON (fe.user_id = u.id)
LEFT JOIN
tbl_favs fa ON (
fa.user_id = u.id
AND
fa.feed_id = fe.id
)
In order to link your tables, you need to find the most common link between them all. This link is user_id. You'll want to create a relationship between all tables with JOIN in order to make sure each and every user has data.
Now I don't know if you're planning on making sure all tables have data with the user_id. But I would use INNER JOIN as it will ONLY show records of that user_id without nulls. If the other tables could POSSIBLY (Not always guaranteed) you should use a LEFT JOIN based on the tables that is it possible with.
Here is an SQLFiddle as an example. However, I recommend you name your ID fields as appropriate to your table's name so that way, there is no confusion!
To get your isFavorite I would use a subquery in order to validate and verify if the user has it selected as a favorite.
SELECT
u.userid,
u.gender,
f.feedsid,
f.feedvalue,
(
SELECT
COUNT(*)
FROM
tbl_favs a
WHERE
a.userid = u.userid AND
a.feedsid = f.feedsid
) as isFavorite
FROM
tbl_users u
INNER JOIN
tbl_feeds f
ON
u.userid = f.userid
~~~~EDIT 1~~~~
In response to your comment, I have updated the SQLFiddle and the query. I don't believe you really need a join now based on the information given. If you were to do a join you would get unexpected results since you would be trying to make a common link between two tables that you do not want. Instead you'll want to just combine the tables together and do a subquery to determine from the favs if it is a favorite of the user's.
SQLFiddle:
SELECT
u.userid,
f.feedsid,
u.name,
u.gender,
f.feedvalue,
(
SELECT
COUNT(*)
FROM
tbl_favs a
WHERE
a.userid = u.userid AND
a.feedsid = f.feedsid
) as isFavorite
FROM
tbl_users u,
tbl_feeds f
ORDER BY
u.userid,
f.feedsid
I have a table in a MySQL DB, called ‘users’. The fields for users are : id, email, username, first_name, last_name. Another table in the same MySQL DB, called ‘premium_users’ , contains 2 fields : user_id, premium_service_id. A third table called ‘premium_services’ contains 2 fields : premium_service_id , premium_service_name.
I want to create an SQL query , to interrogate my db, so i can have a full list of what premium services has every premium user. How can i interrogate properly with inner join? I’ve try this :
select * from users inner join premium_users on users.id = premium_users.user_id inner join premium_services on premium_users.premium_service_id = premium_services.premium_service_id;
Since you say which service has every user, you'll need to use aggregation to determine this. Here's one way:
select user_id
from premium_users
group by user_id
having count(*) = (select count(*) from premium_services)
SQL Fiddle Demo
Depending on your data, you may need count(distinct premium_service_id) instead, but you should have constraints that don't allow duplicates in those table.
Rereading your question, I might have got this backwards. Looks like you want a list of premium services instead of users. Same concept applies:
select ps.premium_service_id
from premium_services ps
join premium_users pu on ps.premium_service_id = pu.premium_service_id
group by ps.premium_service_id
having count(distinct pu.user_id) = (select count(distinct user_Id) from premium_users)
More Fiddle
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;
I have a user table from which I want all values, so I have this query:
SELECT tbl_user.* FROM tbl_user
Now I want one additional column in this result which shows all roles this user has, (or nothing if there are no roles for the user). The role information comes from two additional tables.
The first table contains these two values: userid, roleid
The second table contains roleid and role_name.
So the group concat needs to get all role names based on the roleid's in table1.
I have tried several different ways to do this, but I don't succeed. Either I get only one result with several times the same rolename, or no result at all.
Thanks for your help
Michael
Update: added LEFT JOIN for users with no role.
SELECT
tbl_user.*,
GROUP_CONCAT(role_name) AS roles
FROM
tbl_user LEFT JOIN tbl_roles ON tbl_user.userid = tbl_roles.userid
JOIN tbl_rolenames ON tbl_roles.roleid = tbl_rolenames.roleid
GROUP BY tbl_user.userid
Note that MySQL will permit a GROUP BY on fewer columns than appear in the SELECT list in total, but in other RDBMS you would need to explicitly list out the columns in tbl_user and include them in the GROUP BY, or do an additional self join against tbl_user to get the remaining columns from that table.
Something like:
SELECT
urole.userid,
uall.username,
uall.name,
uall.othercols,
urole.roles
FROM
tbl_user uall JOIN (
SELECT
tbl_user.userid,
GROUP_CONCAT(role_name) AS roles
FROM
tbl_user LEFT JOIN tbl_roles ON tbl_user.userid = tbl_roles.roleid
JOIN tbl_rolenames ON tbl_roles.roleid = tbl_rolenames.roleid
GROUP BY tbl_user.userid
) urole ON uall.userid = urole.userid