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;
Related
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 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
I'm unable to form a query with the following tables, which will find out all the Notes from Note table, which is created by any user, who belongs to the logged in user's same company.
Note:
note_id (int),
note_text (varchar),
created_by (int)
User:
user_id (int),
company_id (int)
Logged in user's user id is passed as parameter to the query.
I want to pick up notes from the table Notes where created_by in (user_id of all users whose company_id = company_id of LOGGED_IN_USER)
Please help me to formulate out the query. Looks pretty straight forward, but just can't reach to it's end.
I'm not sure if LOGGED_IN_USER is a table or another object, but if it is a table with the columns you referenced, a join like this would work.
select note_text
from Note n
JOIN User u ON u.user_id = n.created_by
JOIN LOGGED_IN_USER lin ON lin.user_id = u.user_id
and lin.company_id = u.company_id
u might need a Foreign Key for user_id to Notes. and use INNER JOIN
Thanks Vinnie and all for your responses. I finally succeeded to figure out the query. LOGGED_IN_USER_ID is just a numeric parameter which should be passed to the query.
select n.* from Note n where
n.created_by in (
select u1.user_id from User u1 inner join User u2
on u1.company_id=u2.company_id and u2.user_id = :LOGGED_IN_USER_ID*
)
Thanks again.
If i am not misunderstood your question,Try this way
SELECT note_text
FROM Note n
INNER JOIN User u ON u.user_id = n.created_by
WHERE n.created_by= (select u.user_id from User where company_id=LOGGED_IN_USER LIMIT 1 )
it's been a while since I used SQL so I'm asking sorry if it's too easy.
I have to select all the skills that a user has, so I have three tables.
User (id, name)
Skills (id, name)
User_skills (id_user, id_skill)
If the user1 has 2 skills; for example Hibernate (id 1) and Java (id 2)
and the user2 has 1 skill; Java (id 1)
Passing 1 and 2, I want to retrieve users that have both.
With the IN() function I get all the users that have at least one of the skills, but I want to filter them out!
Thanks to all in advance
If one skill can only be assigned exactly once to a user (i.e. (id_user, id_skill) is the PK for the user_skills table), then the following will do what you want:
SELECT id_user
FROM user_skills
WHERE id_skill IN (1,2)
GROUP BY id_user
HAVING count(*) = 2
Join to the association table user_skills twice, putting the skill ID in the on clause of each join:
select u.*
from user u
join user_skills us1 on us1.id_user = u.id and us1.id_skill = 1
join user_skills us2 on us2.id_user = u.id and us2.id_skill = 2
By using join (and not left join) this query requires the user have both skills
SELECT name FROM user as u
WHERE
EXISTS( SELECT 1 FROM User_skills WHERE id_user=u.id AND id_skill=1 )
AND EXISTS( SELECT 1 FROM User_skills WHERE id_user=u.id AND id_skill=2 )
I have two tables:
Users: ID, first_name, last_name
Networks: user_id, friend_id, status
I want to select all values from the users table but I want to display the status of specific user (say with id=2) while keeping the other ones as NULL. For instance:
If I have users:
? first_name last_name
------------------------
1 John Smith
2 Tom Summers
3 Amy Wilson
And in networks:
user_id friend_id status
------------------------------
2 1 friends
I want to do search for John Smith for all other users so I want to get:
id first_name last_name status
------------------------------------
2 Tom Summers friends
3 Amy Wilson NULL
I tried doing LEFT JOIN and then WHERE statement but it didn't work because it excluded the rows that have relations with other users but not this user.
I can do this using UNION statement but I was wondering if it's at all possible to do it without UNION.
You need to put your condition into the ON clause of the LEFT JOIN.
Select
u.first_name,
u.last_name,
n.status
From users u
Left Join networks n On ( ( n.user_id = 1 And n.friend_id = u.id )
Or ( n.friend_id = 1 And n.user_id = u.id )
Where u.id <> 1
This should return you all users (except for John Smith) and status friend if John Smith is either friend of this user, or this user is friend of John Smith.
You probably don't need a WHERE clause, and instead of that, put the condition into the "ON" clause that follows your "LEFT JOIN". That should fix your issues. Also, make sure that the main table is on the left side of the left join, otherwise, you should use a right join.
In addition to the (correct) replies above that such conditions should go in the ON clause, if you really want to put them in the WHERE clause for some reason, just add a condition that the value can be null.
WHERE (networks.friendid = 2 OR networks.friendid IS NULL)
From what you've described, it should be a case of joining a subset of networks to users.
select id, first_name, last_name, status
from users u
left join networks n on u.id = n.user_id
and n.friend_id = 1
where id <> 1;
The left join will keep rows from users that do not have a matching row in networks and adding the and n.friend_id = 1 limits when the 'friends' status is returned. Lastly, you may choose to exclude the row from users that you are running the query for.