I've got a mysql question that I haven't been able to figure out. Its a little bit different than the other questions I've found here on SO.
I've got three tables
users
____________
ID name
1 John
2 Mike
3 Susie
tasks
___________
ID Name
1 Brush Teeth
2 Shower
3 Check Email
users_tasks
_____________________
ID user_id task_id
1 1 1
2 1 2
3 1 3
4 2 1
5 2 2
6 3 1
Im trying to find out what users haven't completed what tasks yet. I would like the result set to look like this:
user_id task_id
__________________
2 3
3 2
3 3
The closest I have come is this query, which only gives me users that haven't completed at least one of the tasks, but doesn't give me the task.
select * FROM users
right JOIN users_tasks on users.id = users_tasks.user_id
right JOIN tasks on users_tasks.task_id = tasks.id
where tasks.id is null
I cant figure out how to return duplicate users and tasks based on what is missing form the join table.
Thanks in advance
An easy solution is just to require that the entry is not in your completed tasks table:
select * from users, tasks
where not exists (
select * from users_tasks
where users.id = users_tasks.user_id and tasks.id = users_tasks.task_id
);
Result:
+------+-------+------+-------------+
| id | name | id | name |
+------+-------+------+-------------+
| 3 | susie | 2 | Shower |
| 2 | mike | 3 | Check Email |
| 3 | susie | 3 | Check Email |
+------+-------+------+-------------+
One way to do this is to create a set representing the cartesian product of the users and tasks tables. This is what would be the result if every user had done every task. Then do a left join with the actual users_tasks table and filter for null to get the missing items:
select sub.*
from (
select u.id user_id, t.id task_id
from users u, tasks t
) sub
left join users_tasks ut on sub.user_id = ut.user_id and sub.task_id = ut.task_id
where ut.ID is null;
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
I have a table called Users:
UserID | DisplayName
----------------------
2 | Jack
3 | Jill
And a table called Tasks:
TaskID | UserID | UserForID
--------------------------------
1 | 2 | 3
2 | 3 | 2
3 | 3 | 3
Basically in here, users can set tasks for each other or themselves.
My query is as follows:
SELECT *
FROM Tasks
INNER JOIN Users
ON Tasks.UserForID=Users.UserID
Now using $row['DisplayName'] gets the display name of the user the task is for, but how do I go about getting the display name of the user who posted the task?
Join the same user table for both the users. When you joined for first time you joined based on UserForID thats why you were getting only for ForUser, now if you join
SELECT t.TaskID, u.DisplayName as ForUser, tu.DisplayName as FromUser
FROM Tasks t
INNER JOIN Users u ON t.UserForID=u.UserID
INNER JOIN Users tu ON tu.UserID=t.UserID
The key FromUser will contain the name of the user who created the task
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 have the following (simplified) three tables:
user_reservations:
id | user_id |
1 | 3 |
1 | 3 |
user_kar:
id | user_id | szak_id |
1 | 3 | 1 |
2 | 3 | 2 |
szak:
id | name |
1 | A |
2 | B |
Now I would like to count the reservations of the user by the 'szak' name, but I want to have every user counted only for one szak. In this case, user_id has 2 'szak', and if I write a query something like:
SELECT sz.name, COUNT(*) FROM user_reservations r
LEFT JOIN user_kar k ON k.user_id = r.user_id
LEFT JOIN szak s ON r.szak_id = r.id
It will return two rows:
A | 2 |
B | 2 |
However I want to every reservation counted to only one szak (lets say the highest id only). I tried MAX(k.id) with HAVING, but seems uneffective.
I would like to know if there is a supported method for that in MySQL, or should I first pick all the user ID-s on the backend site first, check their maximum kar.user_id, and then count only with those, removing them from the id list, when the given szak is counted, and then build the data back together on the backend side?
Thanks for the help - I was googling around for like 2 hours, but so far, I found no solution, so maybe you could help me.
Something like this?
SELECT sz.name,
Count(*)
FROM (SELECT r.user_id,
Ifnull(Max(k.szak_id), -1) AS max_szak_id
FROM user_reservations r
LEFT OUTER JOIN user_kar k
ON k.user_id = r.user_id
GROUP BY r.user_id) t
LEFT OUTER JOIN szak sz
ON sz.id = t.max_szak_id
GROUP BY sz.name;