I have struggle to produce good SQL.
It is a relationship part of application.
I have 3 tables : users('id'), relationship('user_id', 'member_id'), relationship_block('user_id', 'blocked_member_id')
I would like to get all members belonging to user with user_id that are not blocked.
Records of first table 'users' that are in 'relationships' table but that are NOT in 'relationship_blocked' table.
First 2 i can do with JOIN, but then I want to remove those that are blocked.
Thanx.
edit: found a good info about it here: http://explainextended.com/2010/05/27/left-join-is-null-vs-not-in-vs-not-exists-nullable-columns/
/* this would get the user */
SELECT *
FROM users
WHERE id = $ID
/* build on this to get relationships */
SELECT *
FROM users u
JOIN relationship r ON r.user_id = u.id
WHERE u.id = $ID
/* build on this to get not blocked */
SELECT *
FROM users u
JOIN relationship r ON r.user_id = u.id
JOIN relationship_block b ON b.user_id = u.id
WHERE u.id = $ID
AND r.member_ID <> b.blocked_member_id
/* get all users that NO ONE has blocked */
/* this means if there exists a record b such that b.blocked_member_id
equals the user X has blocked user Y, do not include user Y.
By extension, if X and Y are fierce enemies and have blocked eachother,
neither would get returned by the query */
SELECT *
FROM users u
JOIN relationship r ON r.id = u.id
WHERE NOT EXISTS ( SELECT null
FROM relationship_block rb
WHERE rb.blocked_member_id = u.id
)
/* This runs two queries at once. The inner query says "I'm not getting any
columns, because I don't care about the actual data, I just to get all
records where someone has blocked the user I'm currently looking for".
Then you select all users where that isn't true. For good speed, this would
require an index on relationship_block.blocked_member_id */
select *
from users u
inner join relationship r
on u.user_id = r.user_id
left join relationship_block rb
on r.user_id = rb.user_id
and r.member_id = rb.blocked_member_id
where rb.user_id is null
Related
In my database, I have users, apps, and releases. A user can have 0..n apps through a permissions table and an app can have 0..n releases.
I'm trying to get a list of users who have at least 1 app, but none of that user's apps have any releases.
The schema is roughly
users permissions apps releases
----- ----------- ---- --------
id user_id id id
email app_id app_id
I think I've got something working with this, but it appears inefficient to me because I mention the permissions table twice and I'm using nested exists clauses. Is there a more efficient way to write this query?
select u.email from users u
join permissions p on p.user_id = u.id
where not exists (
select a.id from apps a
join permissions p on p.app_id = a.id
where p.user_id = u.id and exists (
select r.id from releases r
where r.app_id = a.id
)
);
You just need to use a LEFT JOIN on releases, and then look for the case where the number of released apps (r.app_id is non-NULL) is 0. If all you want is a list of users, I don't think you need to JOIN the apps table at all, as JOINing on permissions will ensure that only users that have permission for 1 or more apps are included.
SELECT u.email
FROM users u
JOIN permissions p ON p.user_id = u.id
LEFT JOIN releases r ON r.app_id = p.app_id
GROUP BY u.email
HAVING COUNT(r.app_id) = 0
The first Join seems to be correct between users and permissions table. You just need to check whether the app_id from joined result-set exists in releases table or not. You can try this query -
select u.email from users u
join permissions p on p.user_id = u.id
where not exists ( Select 1 from releases r where r.App_id = p.app_id)
I will do something like this, hope this helps:
SELECT
u.id, u.email
FROM
users AS u
INNER JOIN
permissions AS p ON p.user_id = u.id
LEFT JOIN
releases AS r ON r.app_id = p.app_id
GROUP BY
u.id, u.email
HAVING
SUM(CASE WHEN r.id IS NOT NULL THEN 1 ELSE 0 END) = 0
Another thing you could try is a combination of left and inner joins like this:
Select
email
From users u
Inner Join (
Select
p.user_id
, p.app_id
From permissions p
Left Join releases r
on p.app_id = r.app_id
Where r.app_id is null) a
on u.user_id = a.user_id
Group by email
It's hard to tell which is faster between this and the previous posted solution without knowing the size of the different tables (and hence how many rows SQL will be trying to join).
One thing that is clear - without the 'Group by email' line at the end, you might see users' email repeated multiple times in your list. Generally, literature on SQL states that using a "group by" statement at the end of your query is a faster way to get a distinct set than a "select distinct" statement at the beginning of your query.
I'm trying to gather "followers" for a specific user (#1 in this code).
I'm doing my primary select from followers as the column following will have user #1 and followers.userid will have the userid of the person doing the following.
Next I'm trying to get a count of records from the experiences that have the user id of the follower (how many experiences does this follower have?)
Next, the follower will have rated each experience (1-5 stars) and I want to sum those ratings (experiences.stars) to get an average rating of all experiences.
Lastly, I want to join the followers user record from the users table.
I should end up with
userid, jobs, stars, * from users
SELECT * FROM followers AS F
RIGHT JOIN
(SELECT count(id) FROM experiences AS M WHERE M.userid = F.userid) AS jobs
RIGHT JOIN
(SELECT sum(stars) FROM experiences AS S WHERE S.userid = F.userid) AS stars
RIGHT JOIN
users AS U ON U.userid = F.userid
WHERE F.following = 1 /* #1 = the user # I want the follwers of/for */
I've also tried:
SELECT * FROM followers AS F,
(SELECT count(id) FROM experiences AS M WHERE M.userid = F.userid) AS jobs,
(SELECT sum(stars) FROM experiences AS S WHERE S.userid = F.userid) AS stars
RIGHT JOIN
users AS U ON U.userid = F.userid
WHERE F.following = 1 /* #1 = the user # I want the follwers of/for */
In cPanel, I'm getting an error that I have syntax error at WHERE F.userid in both statements.
A) what am I missing and B) is there a better way to do this?
It seems to me, the query would be easier to follow like so:
SELECT *
FROM followers AS F
LEFT JOIN users AS U ON U.userid = F.userid
LEFT JOIN (SELECT count(id) FROM experiences AS M WHERE M.userid = **F.userid)** AS jobs
LEFT JOIN (SELECT sum(stars) FROM experiences AS S WHERE S.userid = F.userid) AS stars
WHERE F.following = 1 /* #1 = the user # I want the follwers of/for */
;
All those RIGHT JOINs you originally had would only give you followers that had both "types" of experiences.
Also, correlated subqueries can be expensive (and you didn't need two of them...actually, you didn't even need subqueries), so I'd also rework it like so....
SELECT F.*, U.*, count(x.id), sum(x.stars)
FROM followers AS F
LEFT JOIN users AS U ON U.userid = F.userid
LEFT JOIN experiences AS x ON F.userid = x.user_id
WHERE F.following = 1
GROUP BY [all the fields selected in F and U, or just F.userid if server settings allow]
;
Seems like there's a couple of ON clauses missing.
I know that RIGHT outer joins are supported, but why would we write it that way, and not write it as LEFT outer joins. (We typically reserve RIGHT joins to the towers of academia.)
And it's well past time to ditch the old-school comma syntax for join operations. (Yes, it's still supported for backwards compatibility with existing statements. But new development should use the newer JOIN syntax.)
The condition requiring a non-NULL value of F.following would effectively negate the "outerness" of the join, rendering it equivalent to an INNER join. For clarity, we should either write that as an inner JOIN, or if we want an outer join, we should relocate that condition to the appropriate ON clause.
Also, best practice is to qualify all column references; even when they aren't ambiguous to the optimizer, it makes it easier on the future reader (so the future reader doesn't have to confirm which table contains the id column), as well as protecting the query from throwing "ambiguous column" errors in the future if a column named id is added to another table used by the query.
Also, it's not valid to reference columns from F in the outer query inside inline view queries. We can use a correlated subquery, but not as an inline view.
The specification isn't clear. Example data and sample of expected output would go a long ways to clarifying the requirements.
If we want to use correlated subqueries that return a single row, with a single column, we can put those in the SELECT list ...
SELECT f.*
, u.*
, ( SELECT COUNT(m.id)
FROM experiences m
WHERE m.userid = f.userid
) AS jobs
, ( SELECT SUM(s.stars)
FROM experiences s
WHERE s.userid = f.userid
) AS stars
FROM followers f
LEFT
JOIN users u
ON u.userid = f.userid
WHERE f.following = 1 /* #1 = the user # I want the follwers of/for */
ORDER BY ...
We could get an equivalent result using inline views, but that would look quite different.
I would tend to do the aggregation inside the inline view, something along the lines of this:
SELECT f.*
, u.*
, IFNULL(e.jobs,0) AS jobs
, IFNULL(e.stars,0) AS stars
FROM followers f
LEFT
JOIN users u
ON u.userid = f.userid
LEFT
JOIN ( SELECT ef.userid
, COUNT(ee.id) AS jobs
, SUM(ee.stars) AS stars
FROM followers ef
JOIN experiences ee
ON ee.userid = ef.userid
WHERE ef.following = 1 /* argument */
GROUP BY ef.userid
) e
ON e.userid = f.userid
WHERE f.following = 1 /* argument */
ORDER BY ...
I have two tables users and linkage. I am creating a link between one user to another. Means user A will be linked to user B and vise versa.
Now I want to get the details of linked users for a particular entered user_id. Means If user A is finding his linked Id's then the details of linked id's should be seen.
Linkage has three columns its id, user_id and linked_contact_id.
Users has columns as user_id, user_name,pass etc..
I tried one join but I only get the linked Id's from this not the details of id's.
SELECT * FROM Users INNER JOIN linkage ON linkage.user_id = Users.user_id WHERE linkage.linked_contact_id = 1
output
user_id linked_contact_id
1 4
1 1
1 5
How can I get this?Please help.. Thank you...
You will need to join on the users table a second time:
SELECT u.*, u2.* FROM Users u
INNER JOIN linkage l ON l.user_id = u.user_id
INNER JOIN Users u2 ON l.linked_contact_id = u2.user_id
WHERE l.linked_contact_id = 1
Please note that as you are selecting the same columns twice (in u.*, u2.*), you will probably have to list out each field with an alias to distinguish between them.
Something wrong on your ratio. But it's okay.
Try LEFT JOIN or RIGHT JOIN
SELECT * users
LEFT JOIN linkage
ON linkage.user_id = users.user_id
WHERE linkage.linked_contact_id = 1
Get Users information
SELECT users.*,
linkage.*,
contact.user_id as contact_user_id,
contact.user_name AS contact_user_name
FROM users
INNER JOIN linkage ON linkage.user_id = users.user_id
INNER JOIN users AS contact ON linkage.linked_contact_id = contact.user_id
WHERE linkage.linked_contact_id = 1
Edit
Here Screenshot of Query Output
I have this DB structure
* user
user_id
name
* client
client_id
name
* user_client
user_client_id
user_id
client_id
* message
message_id
client_id
description
If there are entries on user_client then the user has permissions restricted to the specific clients listed for his id on the table. If there are no entries, then the user has access to any client.
How can I select only messages that the user can read?
I'm trying to do an IF on the WHERE clause to check if any entries on the user_client table but I don't know where to go from there. It needs to select all messages from any client if no entries on user_client or only messages for client_id specified on user_client table
Thanks for the help!
I would suggest doing two different queries: one for the superusers and the other for the restricted users. Then you can join the two results with a UNION.
SELECT M.message_id,
M.client_id,
M.description
FROM message M
INNER JOIN user_client UC ON (UC.client_id = M.client_id)
INNER JOIN user U ON (UC.user_id = U.id)
WHERE U.id = :user_id
UNION
SELECT M.message_id,
M.client_id,
M.description
FROM message M
WHERE NOT EXISTS (
SELECT *
FROM user_client
WHERE user_id = :user_id
)
You can obtain the same result with other queries but IMHO this one is clearer and more maintainable.
Edit: If you want to ensure that the user exists you should join the second query with the user table.
SELECT M.message_id,
M.client_id,
M.description
FROM message M
JOIN user U
WHERE U.id = :user_id
AND NOT EXISTS (
SELECT *
FROM user_client
WHERE user_id = :user_id
)
One way the do this could be to use two different queries to create a set of the messages users can see and filter according to your needs; something like this should work:
select * from (
select u.user_id, u.name, c.name client, m.message_id, m.description
from user u
join user_client uc on u.user_id = uc.user_id
join client c on uc.client_id = c.client_id
join message m on c.client_id = m.client_id
union all
select u.user_id, u.name, c.name client, m.message_id, m.description
from user u
cross join client c
join message m on c.client_id = m.client_id
where user_id not in (select user_id from user_client)
) x
where x.user_id = 1;
Here users present in the user_client table are restricted to the set of messages that they have access to (the first set in the union), while users not present in the user_client table can see all messages (the second set in the union).
Sample SQL Fiddle
If I am understanding your question correctly, such as
1) Administrative user... They can look at EVERYTHING since they would have no records in the user_client table.
2) Client Supervisor... Such a person who's primary responsibility is to a specific client (or multiple clients). Therefore, the user DOES have a record in the user_client table. If so, then only allow the user to see records for those clients they DO have associations with.
select
m.message_id,
m.client_id,
m.description,
c.name as clientName
from
( select count(*) as HasClients
from user_client
where user_id = TheUserYouWant ) ClientCheck,
message m
left join user_client uc
on m.client_id = uc.client_id
AND uc.user_id = TheUserYouWant
join client c
on m.client_id = c.client_id
where
ClientCheck.HasClients = 0
OR NOT uc.user_id IS NULL
The query looks at the user_client table TWICE. The first time is to just get a count of those records that DO exist for the given user, regardless of which client associated with. The query will always come back with 1 row and it will either be 0 (no such records), or greater than 1 (however many they are associated with).
The second instance is a LEFT-JOIN to the user_client table, JUST IN CASE the person IS restricted to only looking at their own client messages.
The WHERE clause now comes in and says... if the underlying count of clients was zero, then ok to give me all messages. If any other value, then the user ID in the user_client table (as left-joined to the messages on both the CLIENT AND THE USER you want) MUST EXIST (via NOT a NULL value for the user_id column).
Now, you probably don't want to query EVERY message as it could get quite large as your database grows, but you could put whatever other criteria in the WHERE clause, such as date restrictions and/or client(s) you are interested in.
I'm trying to grab all of the offers provided to a user that are not already queued up in their projects. So, I'm grabbing offers from the OfferSuggestionHeader table based on my user's ID but also try to make sure it doesn't grab anything that the user has already added to their projects (stored in the Projects table)
I've got the following query:
SELECT DISTINCT ofh.OfferID, ofh.OfferTitle, ofh.OfferVendor, ofh.Savings,ofh.SavingsPercent
FROM OfferSuggestionHeader ofh
LEFT JOIN OfferSuggestionDetail osd
ON ofh.OfferID = osd.OfferID
LEFT JOIN Facilities f
ON osd.FacilityID = f.id
LEFT JOIN UserFacility uf
ON f.id = uf.fid
LEFT JOIN Users u
ON uf.uid = u.uid
LEFT JOIN Projects p
ON p.uid = u.uid
WHERE p.uid = '1'
AND ofh.OfferID <> ANY (SELECT offer_id FROM Projects WHERE uid = '1')
It pulls up all of the offers. If I take away ANY then I get an error saying that the subquery returns too many results.
There are 6 offers. Three are queued up by user 1. I shouldn't see offers 1, 4, or 5.
Thanks for any pointers and help.
As per my comment explanation, why not try this? I am not sure why you need a subquery when you already have PROJECT table JOINED in your main query..
WHERE p.uid = '1'
AND ofh.OfferID NOT IN (1, 4, 5);