Okay, so I have two tables that I need to link together with a JOIN query. There is a table called likes and a table called users. The users table looks something like this
id name
----- ------
1 Mark
2 Mike
3 Paul
4 Dave
5 Chris
6 John
The likes table looks like this.
user_one user_two match_id
----- ------ --------
1 2 abc
2 1
1 3 acc
3 1 abb
1 5 aee
5 1
The expected result should be
id name
----- ------
1 Mark
The two tables should only be linked on the rows in the likes table where the users_one column is set to the value that is most commonly found in that column. In this case, the user with the id of 1 is in the likes table with the user_one column 3 times where the match_id isn't empty.
I've thought it out to be written something like this
SELECT users.*, likes.COUNT(*) AS count
FROM users
JOIN likes
ON users.id = likes.user_one
WHERE likes.match_id != ''
But, I know this isn't correct. Is there a way to link two tables with a JOIN only on the most common rows in one of the tables?
Would Grouping work for what you need... ?
SELECT users.id, users.name, count(*) AS count
FROM users
JOIN likes
ON users.id = likes.user_one
WHERE likes.match_id != ''
group by users.id, users.name
should give you something like
1 Mark 3
Should be something like this, if I understood the question
select top 1 user_one, name
from likes
inner join users ON users.id = likes.user_one
where match_id != ''
group by user_one
order by count(*) Desc
Are you looking for something like this?
select u.id, u.name, count(*)
from users u
inner join likes l
on l.id = l.user_one and l.match_id != ''
group by u.id, u.name
order by count(*) desc
limit 1
The limit 1, combined with sorting by the # of likes in descending order will result in getting one user - the one with the most matched likes.
Try:
select *
from users
where id in (
select id
from likes
group by id
order by count(*) desc, id
limit 1
)
The subquery returns the id of the row with the most appearances in the likes table (group by id and order by count(*) desc). I've added id to the order by to give predictable results in case there are multiple with the same number of appearances. This is used to join to the users table to give the resultset required.
Related
I need to make one SQL command.
From table with comments i'll get comment id, then
with this ID I need to get count of reactions with the same comment ID and user's names.
So for example I have this 2 tables:
Comments:
ID
Comm_text
1
Example text
2
Another example
and Reactions:
ID
comm_id
usr
etc..
1
1
Peter
another
2
1
John
collon
3
1
Dog
cuz
4
2
Cat
why not
I need to get this:
ID
Comm_text
Reactions_Count
Users
1
Example text
3
Peter, John, Dog
2
Another example
1
Cat
I tried this:
SELECT k.id, k.comm, COUNT(r.id) as reactions, r.usr
FROM `comms` k
INNER JOIN `reactions` r ON r.id=k.id
It's just one row with one comment and count of all rows in reaction table.
Thanks.
Try this query that makes the same output:
select comments.id as ID , comments.Comm_text as Comm_text ,
(select count(id) from Reactions where comm_id = comments.id) as Reactions_Count ,
(select coalesce(GROUP_CONCAT(usr ORDER BY usr DESC) , '') from Reactions WHERE comm_id = comments.id) as Users
from comments group by comments.id
You should use group by to group the comments and have just one row then use query to count and gather the data, based on each row of the group.
The GROUP_CONCAT attach the output with , and the coalesce set the output to a given string if the output was empty.
Read more about:
GROUP BY
GROUP_CONCAT
COALESCE
subquery
According to the names that u set in the example, this will work. Just fix the table names for your database structure.
SELECT `Comments`.`ID`, `Comments`.`Comm_text`, count(`Reactions`.`comm_id`) as react, `Reactions`.`usr`
FROM `Comments`
INNER JOIN `Reactions`
ON `Comments`.`ID`=`Reactions`.`comm_id`
GROUP BY `Reactions`.`comm_id`
In a MySQL 5.7 database, I have the following User table:
Name
Id
David
1
Frank
2
And the following Order table:
Id
Price
UserId
1
55
1
2
68
1
3
50
1
4
10
2
For every user, I want to select the price of the order with the biggest ID.
I can use the following query which adds additional complexity due to the nested subquery :
SELECT
User.Name,
last_user_order.Price
FROM User
LEFT JOIN (
SELECT Price, UserId FROM Order
ORDER BY Id DESC LIMIT 1
) AS last_user_order ON last_user_order.UserId = User.Id
There exist many questions here where the column to be selected is the same than the one being ordered. Hence, it is possible to use MAX in the first SELECT statement to avoid a subquery. Is it possible to avoid a subquery in my case?
For every user, I want to select the price of the order with the biggest ID.
That looks like:
SELECT
u.*,
o.Price,
FROM
User u
INNER JOIN Order o ON u.ID = o.UserID
INNER JOIN
(
SELECT MAX(ID) as OrderID FROM Order GROUP BY UserId
) maxO ON o.Id = maxO.OrderId
SELECT User.Name,
( SELECT Order.Price
FROM Order
WHERE Order.UserId = User.Id
ORDER BY Order.Id DESC LIMIT 1 ) LastPrice
FROM User;
I have three tables and Im trying to count the number of likes per user on all his/her post.
USER TABLE
id name
1 John
2 Joe
POSTS TABLE
id user_id post_title
1 1 Some Title
2 1 Another Title
3 2 Yeah Title
LIKES TABLE
id post_id
1 1
2 1
3 1
4 2
5 3
My expected output is
ID LIKES
1 4
2 1
Im kinda stuck with the code below. I don't know how to add and count the likes table.
SELECT *
FROM user
INNER JOIN posts
ON user.id = posts.user_id;
You need to extend the join to the LIKES table and then use GROUP BY to group by the user ID and COUNT() all of the records for that user...
SELECT user.id, COUNT(likes.id)
FROM user
INNER JOIN posts ON user.id = posts.user_id
INNER JOIN likes ON posts.id = likes.post_id
GROUP BY user.id
If you want to list people who don't have posts or likes, then you should use outer joins (so change INNER JOIN to LEFT JOIN) so that these users show up.
For your desired result, you don't need the user table. You can simply do:
SELECT p.user_id, COUNT(*)
FROM posts p JOIN
likes l
ON l.post_id = p.id
GROUP BY p.user_id;
The only information you are taking from users is the id, which is already in posts. This assumes that all the user_id values in posts are valid, but that seems like a very reasonable assumption.
As I'm SQL beginner, I can't describe a problem in a simple way, so let me show you an example:
3 Tables:
PRODUCT
id
group_id
person_id
GROUP
id
name
PERSON
id
group_id
As you see, GROUP can have multiple PERSONs and PRODUCT can be connected with GROUP and PERSON.
From this point, I would like to count number of PERSONs having a PRODUCT within a GROUP
I don't really understand the background of IN or using another SELECT within FROM, so if that's the point, then I'm happy that I was one step before it lol.
SELECT
group.name as GROUP_name,
COUNT(DISTINCT person_id) AS PERSON_having_min_one_PRODUCT
FROM products
LEFT JOIN groups ON groups.id = products.group_id
LEFT JOIN persons ON persons.id = products.person_id;
With this data:
GROUP
ExampleGroupName1 has 3 PERSONs, but 2 of them has >0 PRODUCTS
ExampleGroupName2 has 3 PERSONs and all of them has >0 PRODUCTS
ExampleGroupName3 has 2 PERSONs, but none of them has the PRODUCT
ExampleGroupName4 has 2 PERSONs, but only 1 has >0 PRODUCT
I would like to have an output like this:
GROUP_name | PERSON_having_min_one_PRODUCT
ExampleGroupName1 | 2
ExampleGroupName2 | 3
ExampleGroupName4 | 1
I would like to count number of PERSONs having a PRODUCT within a GROUP
Note: I will assume the table product does not have the column group_id, since it is redundant and can lead to a lot of errors.
The following query will show you the result you want by joining the tables person and product:
select
count(distinct x.id)
from person x
join product p on p.person_id = x.id
where x.group_id = 123 -- choosing a specific group
and p.id = 456 -- choosing a specific product
This would rather be simple like below meaning all the groups with some group_id with count(persons) and those count who has some product via id used in having clause
Select group_id,
count( distinct id ) AS "PERSON_WITH_PRODUCT"
from
person group by group_id having id
in (Select id from product);
I have a table users containing the fields userID,age,gender and i have another table
name as click_info containing fields(id,userID,clickID) The enrty in the click_info table are as following
id userID dubID
1 1 2
2 1 2
3 1 2
4 2 2
5 2 2
6 3 2
7 4 2
Now I want the average age of all the users who clicked on dubID 2 and i am using the following query
SELECT DISTINCT `dub_clickinfo`.`userID`, `users`.`age` AS `average`, `users`.*
FROM `dub_clickinfo` INNER JOIN `users` ON dub_clickinfo.userId = users.userID
WHERE (dubID=2)
The above query gives the incorrect average it will include the duplicate userID (like it will include userID 1 three times,2 two times) as well.
Please suggest a query
Thanks In Advance !!
Give it a try ,there is a one to many relation so you need to use left join not inner ,and apply a group function on user's id
SELECT dub_clickinfo.userID, users.age AS average, users.* FROM dub_clickinfo
LEFT JOIN users ON dub_clickinfo.userId = users.userID WHERE (dubID=2)
GROUP BY users.userID
try this
SELECT avg(age) FROM users WHERE userID in (select distinct userID from dub_clickinfo where dubID ='2')