Firstly, I'm not even sure if LEFT JOIN is the best way of doing what I want to do, so will try best to explain.
I have 2 tables - one containing a list of sites, and another containing a list of roles. A user may just have one role, but they may have as many roles as there are sites.
Table 'sites'
site_id | site_name | site_domain
---------------------------------------
1 | Site A | sitea.com
2 | Site B | siteb.com
Table 'roles'
site_id | user_id | role_id
---------------------------------
1 | 1 | 1
1 | 2 | 1
2 | 2 | 2
As in my example above, User 1 has just one role on just one site, but User 2 has two roles on two different sites.
What I'd like to do, and it's probably just a Sunday night not thinking straight kinda thing, is to get a list of sites out, along with the role for each individual user - if no role exists for that site for a user, then return NULL (or 0).
Two examples of how the output should result:
User 1
site_id | site_name | site_domain | role_id
----------------------------------------------
1 | Site A | sitea.com | 1
2 | Site B | siteb.com | NULL
User 2
site_id | site_name | site_domain | role_id
----------------------------------------------
1 | Site A | sitea.com | 1
2 | Site B | siteb.com | 2
The query I have at the moment is below, however, the 2nd site does not appear since the user doesn't have a role defined (ie. like above, but for User 1 the 2nd Site B will not list). I know I'm just missing something but cannot think of it tonight :o(
SELECT site_id, site_name, site_domain, role_id
FROM `sites`
LEFT JOIN `roles`
ON sites.site_id=roles.site_id
WHERE roles.user_id='1'
What you need to do is start with a table that combines all sites and users. Then join in the information in the roles table:
select s.site_id, s.site_name, s.site_domain, u.user_id, r.role_id
from (select distinct user_id from roles) u cross join
sites s left outer join
roles r
on s.site_id = r.site_id and
u.user_id = r.user_id
If you have a users table, then you can replace the first subquery with that table.
For the sites where a single user is involved, you can just put a constant in the subquery:
select s.site_id, s.site_name, s.site_domain, u.user_id, r.role_id
from (select 1 as user_id) u cross join
sites s left outer join
roles r
on s.site_id = r.site_id and
u.user_id = r.user_id
Or a where clause: where u.user_id = 1.
Related
I want to use an join to list the car colors count, car type, and users name.
I have 3 table
Table 1 Useres
id|username|fullname
1 | test0 | xy xy
2 | test1 | yx yx
Table 2 Car Type
id|car_type|user_id
1 | Ford | 1
2 | BMW | 2
3 | Ford | 1
4 | Skoda | 1
5 | BMW | 2
Table 3 Car Color
id| Color |user_id|car_id
1 | Red | 1 |1
2 | Blue | 2 |2
3 | Red | 2 |5
4 | Red | 1 |3
5 | Red | 1 |4
6 | Green | 1 |4
One car has 2 color
The result should be:
countType | CountColor | UserName
3 | 4 | test0
2 | 2 | test1
I tryed this:
SELECT
test as BlogsPost,
test2 as CommenstPost,
u.name
FROM users u
LEFT JOIN (
select COUNT(blogs.user_id) as test FROM blogs GROUP by blogs.user_id) blogs
on blogs.user_id=u.id
LEFT JOIN (
select COUNT(comments.user_id) as test2 FROM comments GROUP by comments.user_id) comments
on comments.user_id=u.id
GROUP by users.id
If I understand your question correctly with reference to your actual code section what you want is a list of users with how many blogs they have and how many comments they have. Now if you were wanting to count one matching table you could just do this:
SELECT
U.NAME
,COUNT(1) AS BLOG_COUNT
FROM USERS U
LEFT JOIN BLOGS B
ON B.USER_ID = U.ID
GROUP BY U.NAME
But since you are wanting to count two tables you have to do it slightly differently. There's a few ways of doing it but the way I like is like this:
SELECT
U.NAME
,B.BB_COUNT AS BLOG_COUNT
,C.CC_COUNT AS COMMENT_COUNT
FROM USERS U
LEFT JOIN
(
SELECT
BB.USER_ID
,COUNT(1) AS BB_COUNT
FROM BLOGS BB
GROUP BY BB.USER_ID
) B
ON B.USER_ID = U.ID
LEFT JOIN
(
SELECT
CC.USER_ID
,COUNT(1) AS CC_COUNT
FROM COMMENTS CC
GROUP BY CC.USER_ID
) C
ON C.USER_ID = U.ID
That may or may not be the most efficient way but in my experience it works pretty well and it's simple to understand. It all depends a lot on the number of rows in the tables and indexes etc. Usually the idea is to narrow down rows returned as fast as possible. In this case you'll have two sub queries but they'll end up with only as many rows as you have users basically.
Another thing to note, this will return all users, period. That may not be what you want. You might want only a subset of users. If so this inner select may not be the most efficient because you're doing calculations on users that may not be in the final result, wasting time. However I may be getting off topic.
I agree with the comment that states the table design is not really well constructed yet for you to achieve the counts you want you will need to do subqueries like this:
SELECT
(SELECT count(1) from CarType where user_id=username) as countType,
(SELECT count(1) from CarColor where user_id=username) as countColor,
username from (
SELECT username from Users
) a
As a suggestion for design:
Table Users
Table Cars
Table Colors
Then you have a Relationship table where you have user_id, car_id, color_id
This would be the proper table design for this structure
This may be simple for some, but I cannot work it out.
I have 3 tables:
Teams, Users, Tags
Teams Users Tags
------------------- ------------------ -----------------------
userID | teamUserID userID | username userID | name | value
------------------- ------------------ -----------------------
1 | 2 1 | dan 2 | myTag | 1
1 | 3 2 | bob 2 | aTag | 2
1 | 4 3 | jon 3 | bTag | 1
4 | rob 4 | cTag | 5
Each team can have a number of users in it, and each user can own a number of tags.
I need a query which will provide a list of users in any given team, with a total number of tags they have.
So when I request results from team 1 (dan's team) it should return this:
-----------------------------------
userID | username | tagTotalValue
-----------------------------------
2 | bob | 3
3 | jon | 1
4 | rob | 5
I have this query so far, but it just gives me one record with an overall total for the whole team, rather than a list of all the users in the team separately with their totals.
SELECT username, SUM(value) tagTotalValue
FROM users u LEFT JOIN tags t
ON u.userID = t.userID
WHERE u.userID IN (SELECT teamUserID FROM teams WHERE userID = 1)
Help!
If anyone can explain a good way of working out how to build these queries, I would be very grateful to learn. Do I just need to do a mySQL course, or is there a simple method I can employ?
I need a query which will provide a list of users in any given team,
with a total number of tags they have.
This seems to have little to do with the query you have written. You should start by joining the three tables together and then aggregating. The query looks something like this:
SELECT t.teamId, u.userId, u.username, count(ta.userId) as numTags
FROM teams t JOIN
users u
ON t.teamUserID = u.UserId LEFT JOIN
tags ta
ON u.userID = ta.userID
WHERE t.teamId = #teamId -- this can be removed
GROUP BY t.teamId, u.userId, u.username;
This query makes the leap that teams has a column that identifies the team -- say teamId.
I have 3 tables i want to join all tables each other. But my 3rd table not working.
See my table -
users
id | username |is_active
----------|----------------|------------
1 | chinu | 1
2 | sradhanjali | 1
3 | User3 | 0
settings
id | user_id | public_msg_notification
----------|-----------|---------------------------
1 | 1 | 1
2 | 2 | 1
3 | 3 | 1
friends
id | user_id | friend_id | is_block
----------|-----------|---------------------------
1 | 3 | 1 | 0
2 | 1 | 2 | 1
3 | 3 | 2 | 0
Query
SELECT a.username FROM users a
JOIN settings b
JOIN friends c ON(a.id=c.user_id OR a.id=c.friend_id)
WHERE a.username IN('john','piter','rahul','sradhanjali')
AND a.id != '1' AND a.is_active=1
AND a.id=b.user_id AND b.public_msg_notification=1
AND c.is_block=0 GROUP BY a.username
I have run this query in my local only sradhanjali username fetched. But this user is_block=1 in the friends table.
I think My third table friends not working. I want to show that result those usernmes where is_block=0. In above data my output should be zero(0) But I am getting 1 record while execute above query.
We had a chat discussion and I think this question is not meant to be on SO for the most part. I did promise if I could figure it out I would try to provide some insight. At this point I think this is a correct approach, but it is very specific to this instance.
SELECT u.username FROM users u
JOIN (SELECT
IF(u.id=f.user_id, f.friend_id, f.user_id) as ids
FROM users u
JOIN friends f ON (f.user_id=u.id OR f.friend_id=u.id)
WHERE
u.id=$SOME_ID AND f.is_block=0) friends ON (u.id=friends.ids)
JOIN settings s ON (s.user_id=friends.ids)
WHERE s.public_msg_notification=1 AND u.is_active=1
GROUP BY friends.ids
By trying to be too specific you aren't able to open up the query any more and have to do a nested query inside. This should get all users you are friends with THEN see which users are accepting public notifications and are active. I'm fearing this will fail. But this at the least will put you in the right direction.
I am trying to create a SELECT statement, but I am not really sure how to accomplish it.
I have 2 tables, user and group. Each user has a userid and each group has a ownerid that specifies who owns the group. Each group also has a name and then inside the user table, there is a column group designating which group that person belongs to. (excuse the annoying structure, I did not create it). I am trying to find all rows in group where the ownerid of that group does not have group (inside the user table) set to the name of that group. If this helps:
User
|-----------------------|
| id | username | group |
|----|----------|-------|
| 0 | Steve | night |
| 1 | Sally | night |
| 2 | Susan | sun |
| 3 | David | xray |
|-----------------------|
Group
|---------------------|
| ownerid | name |
|---------|-----------|
| 1 | night |
| 3 | bravo |
| 2 | sun |
|---------------------|
Where the SQL statement would return the group row for bravo because bravo's owner does not have his group set to bravo.
This is a join back to the original table and then a comparison of the values:
select g.*
from group g join
user u
on g.ownerid = id
where g.name <> u.group;
If the values can be NULL, then the logic would need to take that into account.
An anti-join is a familiar pattern:
SELECT g.*
FROM `Group` g
LEFT
JOIN `User` u
ON u.group = g.name
AND u.id = g.ownerid
WHERE u.id IS NULL
Let's unpack that a bit. We're going to start with returning all rows from Group. Then, we're going to "match" each row in Group with a row (or rows) from User. To be considered a "match", the User.id has to match the Group.ownerid, and the User.group value has to match the Group.name.
The "trick" is to eliminate all rows where we found a match (that's what the WHERE clause does), and that leaves us with only those rows from Group that didn't have a match.
Another way to obtain an equivalent result using a NOT EXISTS predicate
SELECT g.*
FROM `Group` g
WHERE NOT EXISTS
( SELECT 1
FROM `User` u
WHERE u.group = g.name
AND u.id = g.ownerid
)
This is uses a correlated subquery; it usually doesn't perform as fast as a join.
Note that these have the potential to return a slightly different result than the query from Gordon Linoff, if you had a row with in Group that had an ownerid value that wasn't in the user table.
SELECT G.*
FROM Group AS G
WHERE G.Name NOT IN (SELECT DISTINCT U.Group FROM User AS U)
So I have two tables, one containing user info (Users), and the other containing info of which users not to show (Settings). So, I want to do a query that will show all the users in the users table except the ones listed in the settings. Thanks in advance.
Users
| id | name |
===============
| 1 | adam |
| 2 | alex |
| 3 | andrew|
Settings
| id | name | value | user_id |
===============================
| 1 | hide | 1 | 1 |
I want the results to be :
| id | name |
==============
| 1 | alex |
| 2 | andrew|
Something like:
SELECT * FROM users WHERE id NOT IN (SELECT user_id FROM settings WHERE name="hide");
would get only the users from the users table which are not in the settings table where the setting name equals "hide"
To get list of something present in one table, but not in another (related) one, you can either use the famouse LEFT JOIN-NULL combo:
SELECT u.id, u.name
FROM users AS u
LEFT JOIN settings AS s
ON s.user_id = u.id
WHERE s.user_id IS NULL
... or NOT IN clause on dependent sub-query:
SELECT u.id, u.name
FROM users AS u
WHERE u.id NOT IN (SELECT user_id FROM settings)
I usually use the first one, but according to this article, there should not be any significant speed difference between those. Anyway, I'd suggest benchmarking them on your specific DB instance, then choosing the best one.
SELECT * FROM users WHERE id NOT IN (SELECT * FROM settings)
try this
SELECT * FROM users WHERE id NOT IN (SELECT user_id FROM settings WHERE user_id='1');