I have tables users and topics. Every user can have from 0 to several topics (one-to-many relationship).
How I can get only those users which have at least one topic?
I need all columns from users (without columns from topics) and without duplicates in table users. In last column I need number of topics.
UPDATED:
Should be like this:
SELECT user.*, count(topic.id)
FROM ad
LEFT JOIN topic ON user.id = topic.ad
GROUP BY user.id
HAVING count(topic.id) > 0;
but it takes 0 result. But it should not be 0.
Firstly you need to have your two tables, because you have left limited information about your table structure I will use an example to explain how this works, you should then be able to easily apply this to your own tables.
Firstly you need to have two tables (which you do)
Table "user"
id | name
1 | Joe Bloggs
2 | Eddy Ready
Table "topic"
topicid | userid | topic
1 | 1 | Breakfast
2 | 1 | Lunch
3 | 1 | Dinner
Now asking for a count against each user is done using the follwing;
SELECT user.name, count(topic.topicid)
FROM user
INNER JOIN topic ON user.id = topic.userid
GROUP BY user.name
If you use a left join, this will include records from the "user" table which does not have any rows in the "topic" table, however if you use an INNER JOIN this will ONLY include users who have a matching value in both tables.
I.e. because the user id "2" (which we use to join) is not listed in the topic table you will not get any results for this user.
Hope that helps!
use inner join and distinct
select distinct user_table.id
from user_table
inner join topics_table on topic_table.user_id = user_table.id
select u.id
, u.name
, count(b.topicName)
from user u
left join topic t on t.userid = u.id
group by u.id, u.name
You can select topic number per user and then join it with user data. Something like this:
with t as
(
select userid, count(*) as n
from topic
group by userid
)
SELECT user.*, t.n
FROM user
JOIN t ON user.id = t.userid
Related
User
USER_ID USERNAME
1 -
2 Chris
3 Dave
4 Vlad
Issue
Creator RESOLVER VERIFIER
2 3 4
2 3 1
3 1 1
expected output:
Creator RESOLVER VERIFIER
Chris Dave Vlad
Chris Dave -
Dave - -
current code I have:
SELECT creatorid.username, resolverid.username, verifierid.username
FROM issue
JOIN user creatorid ON issue.creator = creatorid.user_id
JOIN user resolverid ON issue.resolver = resolverid.user_id
JOIN user verifierid ON issue.verifier = verifierid.user_id
do i have to join the table 3 times to get the corresponding username of the user_id in issue table or is there is a simpler way of doing this? Asking as this is a simplified version of the tables, the User and Issue table contains a lot of other columns. Thanks
Because of the join, you will see each issue three times which is not what you want. You could use three scalar subqueries to get around that:
select i.id,
(select username from users u1 where u1.user_id = i.creator) as creator,
(select username from users u2 where u2.user_id = i.resolver) as resolver,
(select username from users u3 where u3.user_id = i.verifier) as verifier
from issue i;
This isn't going to be fast though.
Another option is to aggregate all user_id / username pairs into a JSON object, then use that in a sub-query:
select i.id, -- other columns from the issue table
u.names ->> i.creator::text as creator,
u.names ->> i.resolver::text as resolver,
u.names ->> i.verifier::text as verifier
from issue i
join lateral (
select jsonb_object_agg(user_id, username) as names
from users u
where u.user_id in (i.creator, i.resolver, i.verifier)
) u on true;
The traditional way to do this is:
select i.*, uc.username, ur.username, uv.username
from issue i left join
users uc
on uc.user_id = i.creator left join
users ur
on ur.user_id = i.resolver left join
users uv
on uv.user_id = i.verifier;
I've got two tables, Job and User, and am trying to pull together some records. Job needs to be joined with User, and User to itself. The structure is:
JobID | OwnerID | ClientName
1 | 1 | Corey
-----------------------------
UserID | ManagerID | Name | Email
1 | 2 | Jon Smith | job#test.com
2 | | Jane Doe | jane#test.com
I'm looking to obtain a table that contains the manager's email address, in addition to the user's name. My query is:
SELECT
Job.ClientName as 'ClientName',
U1.Name as 'SalesPersonName',
U2.Email as 'ManagerEmail'
FROM
Job
INNER JOIN User U1 ON Job.OwnerID = U1.UserID
INNER JOIN User U2 ON U1.UserID = U2.ManagerID
WHERE
Job.ID = '1'
This pulls all Job data, and all data for U1...but is failing to populate U2 - the manager's information.
I imagine I've got something messed up with the self-join. The query validates, so I'm at a loss for what it is.
Any guidance is greatly appreciated.
Note: the above table/column names have been simplified to protect the innocent.
It looks like you juxtaposed the table aliases on the fields in your last JOIN:
This: FULL JOIN User U2 ON U1.UserID = U2.ManagerID
Should be this: FULL JOIN User U2 ON U2.UserID = U1.ManagerID
Full query:
SELECT
Job.ClientName as 'ClientName',
U1.Name as 'SalesPersonName',
U2.Email as 'ManagerEmail'
FROM
Job
FULL JOIN User U1 ON Job.OwnerID = U1.UserID
FULL JOIN User U2 ON U2.UserID = U1.ManagerID
WHERE
Job.ID = 1 --removed ticks here, assuming int column
Note: You don't need a FULL JOIN unless there are records that won't join together, and you want to preserve those records with NULL values in your result set. For the example provided, a basic INNER JOIN would work, but maybe you need the FULL JOIN for your true data set so I left it in.
Note 2: user is a reserved word in many DBMS and could cause you headaches if used as a tablename
I have a User table that has a many to many relationship with Areas. This relationship is stored in the Rel_User_area table. I want to show the user name and the first area that appears in the list of areas.
Ex.
User
id | Name
1 | Peter
2 | Joe
Area
id | Name
1 | Area A
2 | Area B
3 | Area C
Rel_User_area
iduser | idarea
1 | 1
1 | 3
2 | 3
The result I want:
User Name | Area
Peter |Area A
Joe |Area C
Using the minimum area id to determine "First" you could use a correlated subquery (A subquery that refers to field(s) in the main query to filter results):
SELECT user.name, area.name
FROM
user
INNER JOIN Rel_User_Area RUA ON user.id = RUA.iduser
INNER JOIN Area ON RUA.idarea = area.id
WHERE area.id = (SELECT min(idarea) FROM Rel_User_Area WHERE iduser = RUA.iduser)
There's other ways of doing this that may be RDBMS specific. Like in Teradata I would use a QUALIFY clause that doesn't exist in MySQL, SQL Server, Oracle, Postgres, etc.. Regardless of the RDBMS the above should work.
SELECT user.name, area.name
FROM
user
INNER JOIN Rel_User_Area RUA ON user.id = RUA.iduser
INNER JOIN Area ON RUA.idarea = area.id
QUALIFY ROW_NUMBER() OVER (PARTITION BY user.id ORDER BY area.id ASC) = 1;
using the ID from Rel_user_Area you mentioned in comments...
This should be pretty platform independent.
SELECT U.name as Username, A.Name as Area
FROM (SELECT min(ID) minID, IDUser, IDarea
FROM Rel_user_Area
GROUP BY IDUser, IDarea) UA
INNER JOIN User U
on U.ID = UA.IDuser
INNER JOIN Area A
on A.ID = UA.IDArea
If Cross apply and top work (could substitute limit 1 vs top if Postgresql or mySQL)
This will run the cross apply SQL once for each record in user; thus you get the most recent rel_user_Area ID per user.
SELECT U.name as Username, A.Name as Area
FROM User U
on U.ID = UA.IDuser
CROSS APPLY (SELECT TOP 1 IDUser, IDArea
FROM Rel_user_Area z
WHERE Z.IDUSER = U.ID
ORDER BY ID ASC) UA
INNER JOIN Area A
on A.ID = UA.IDArea
I'm very new to SQL so if there are multiple possibilities I'd like to see them all (and hear which possibilities are better than others). I'm using sqlite3.
I have the following 3 tables: user, channel, subscriptions
user:
user_id name
1 Johnny
2 Stacy
3 Allana
channel:
channel_id channel_name
1 ESPN
2 Disney
subscriptions:
user_id channel_id
1 1
2 2
3 1
3 2
What SQL command do I need to perform to get the following table? I basically want to see who is subscribed to which channels by names (so exactly what's laid out in the subscriptions table but mapping numbers to names based on the other tables).
user_id channel_id
Johnny ESPN
Stacy Disney
Allana ESPN
Allana Disney
I've tried the following but I'm getting nothing in the return statement:
select user.name, channel.channel_name from user, channel, subs where user.user_id == subs.user_id and channel.channel_id == subs.channel_id
Try this out and let me know in case you face any difficulty.
select a.name,c.channel_name
from
user a
left join
subscriptions b
on a.user_id = b.user_id
left join
channel c
on b.channel_id = c.channel_id;
or (in the format u asked in comments)
select u.name,c.channel_name
from
user u
left join
subscriptions s
on u.user_id = s.user_id
left join
channel c
on s.channel_id = c.channel_id;
Haven't tested it but try this:
select
u.name
,c.channel
from
user_id u
inner join subscriptions s
on u.user_id=s.user_id
inner join channel c
on s.channel_id=c.channel_id
I have two tables (Users and Pairs). The Pairs table contains 3 columns, an ID and then a user1ID and user2ID.
Users
ID firstName surname
------------------------------
1043 john doe
2056 jane doe
Pairs
ID user1ID user2ID
------------------------------
1 1043 2056
I'm then looking at using a select statement to get the user details base on the ID of the Pairs table:
SELECT users1.*, users2.*
FROM Pairs
JOIN Users users1 ON Pairs.user1ID = users1.IDNumber
JOIN Users users2 ON Pairs.user2ID = users2.IDNumber
WHERE Pairs.ID = 1
Which returns the right details for the two users, however they're all on one row, how can I get it to return each user on a separate row as they are in the Users table?
SELECT users1.*, users2.*
FROM Pairs
JOIN Users
ON Pairs.user1ID = users.IDNumber
OR Pairs.user2ID = users.IDNumber
WHERE Pairs.ID = 1
Just use an OR statement in your ON condition instead of 2 joins.
IN will work also.
SELECT *
FROM Pairs p
JOIN Users u ON u.ID IN (p.user1ID, p.User2ID)
WHERE p.ID = 1