I have two tables, in one table is news in another is images linked with id from news
news
id
title
main_image
services
1
New title
path_to_image_main_image
Photo
2
New title 2
path_to_image_main_image
Photo
images
id
file_name
new_id
1
IMG_8045.jpg
1
2
IMG_8046.jpg
1
3
IMG_8047.jpg
2
4
IMG_8048.jpg
2
5
IMG_8049.jpg
2
new_id is id from news table
My SQL query is
SELECT n.id, n.title, n.main_image, n.services, i.file_name FROM news AS n INNER JOIN images AS i ON n.id = i.new_id
I need to limit this query with 2 images from images table per id from news table
By MySQL version 10.5 I assume you mean MariaDB version 10.5... seeing as MySQL is only on version 8.0 at the moment ;)
I'm not too familiar with the syntax differences between MySQL and MariaDB, but here's a query that works in MySQL 8.0... which technically should work for you in MariaDB 10.5 (seeing as they've had window functions since 10.2 - https://mariadb.com/kb/en/window-functions-overview/)
SELECT
r.*
FROM
(
SELECT
n.id,
n.title,
n.main_image,
n.services,
i.file_name,
ROW_NUMBER() OVER (PARTITION BY i.new_id ORDER BY i.id) AS row_num
FROM news n
INNER JOIN images i ON i.new_id = n.id
) r
WHERE r.row_num <= 2;
Hope this helps :)
I have a solution that supports MySQL 5.6. It is such a mess but it works. I hope performance is not an issue.
Basically it runs the JOIN first time, grouping by id of first table concatenating the ids of second table as a comma separated list. Then do the original join limiting to the list of ids.
Substitute users with news and history with images to name your tables.
SELECT *
FROM
`users` AS u
LEFT JOIN `history` AS h ON u.id = h.user_id
WHERE
FIND_IN_SET(h.id, (SELECT `list` FROM
(SELECT user_id, SUBSTRING_INDEX(GROUP_CONCAT(id SEPARATOR ','), ',', 3) AS `list` FROM
(SELECT h.user_id, h.id
FROM
`users` AS u
LEFT JOIN `history` AS h ON u.id = h.user_id
) AS `a`
GROUP BY user_id
) AS `b`
WHERE b.user_id = u.id
) )
Related
I am trying to find pairs of users who liked the same pages and list the ones who have the most common page likes at the top.
For simplicity I am considering the following table schema
Likes (LikeID, UserID)
LikeDetail (LikeDetailID, LikeID, PageID)
I am trying to find pairs of users with most number of common page likes ordered descending. E.g User1 and User2 have liked 3 pages in common.
I would to have the resulting set of the query to be
UserID1 UserID2 NoOfCommonLikes
2 3 10
4 3 8
1 5 4
I am guessing it would need aggregation, join and aliases however I needed to rename a table twice using AS which did not work for me.
Any tip would be appreciated in MySQL, or SQL Server.
In SQL Server and MySQL 8+, you can use a CTE which JOINs the Likes and LikeDetail table, and then self-JOIN that where PageID is the same but UserID is not, and then grouping on the two userID values:
WITH CTE AS
(SELECT l.UserId, d.PageID
FROM Likes l
JOIN LikeDetail d ON d.LikeID = l.likeID)
SELECT l1.UserId AS UserID1, l2.UserID AS UserID2, COUNT(*) AS NoOfCommonLikes
FROM CTE l1
JOIN CTE l2 ON l2.PageID = l1.PageID AND l2.UserID < l1.UserID
GROUP BY l1.UserID, l2.UserID
ORDER BY COUNT(*) DESC
In versions of MySQL prior to 8.0, you need to repeat the CTE defintion twice in a JOIN to achieve the same result:
SELECT l1.UserId AS UserID1, l2.UserID AS UserID2, COUNT(*) AS NoOfCommonLikes
FROM (SELECT l.UserId, d.PageID
FROM Likes l
JOIN LikeDetail d ON d.LikeID = l.likeID) l1
JOIN (SELECT l.UserId, d.PageID
FROM Likes l
JOIN LikeDetail d ON d.LikeID = l.likeID) l2 ON l2.PageID = l1.PageID AND l2.UserID < l1.UserID
GROUP BY l1.UserID, l2.UserID
ORDER BY COUNT(*) DESC
Note that we use < in the UserID comparison rather than != to avoid getting duplicate rows (e.g. for (UserID1, UserID2) = (1, 2) and (UserID1, UserID2) = (2, 1).
I've made a small demo on dbfiddle which demonstrate the queries.
I have a database with tree tables,
person: id, bio, name
book: id, id_person, title, info
file: id, id_book, location
Other information: Book is about ~50,000 rows, File is about ~ 300,000 rows.
What I'm trying to do is to select 12 different authors and select just one book and from that book select location from the table file.
What I tried is the following:
SELECT DISTINCT(`person`.`id`), `person`.`name`, `book`.`id`, `book`.`title`, `book`.`info`, `file`.`location`
FROM `person`
INNER JOIN `book`
ON `book`.`id_person` = `person`.`id`
INNER JOIN `file`
ON `file`.`id_book` = `book`.`id`
LIMIT 12
I have learned that the DISTINCT does not work the way one might expect. Or is it me that I'm missing something? The above code returns books from the same author and goes with the next one. Which is NOT what I want. I want 1 book from each one of the 12 different authors.
What would be the correct way to retrieve this information from the database? Also, I would want to retrieve 12 random people. Not people that are stored in consecutive order in the database,. I could not formulate any query with rand() since I couldn't even get different authors.
I use MariaDB. And I would appreciate any help, especially help that allows to me do this with great performance.
In MySQL, you can do this, in practice, using GROUP BY
SELECT p.`id`, p.`name`, b.`id`, b.`title`, b.`info`, f.`location`
FROM `person` p INNER JOIN
`book` b
ON b.`id_person` = p.`id` INNER JOIN
`file` f
ON f.id_book = b.id
GROUP BY p.id
ORDER BY rand()
LIMIT 12;
However, this is not guaranteed to return the non-id values from the same row (although it does in practice). And, although the authors are random, the books and locations are not.
The SQL Query to do this consistently is a bit more complicated:
SELECT p.`id`, p.`name`, b.`id`, b.`title`, b.`info`,
(SELECT f.location
FROM file f
WHERE f.id_book = b.id
ORDER BY rand()
LIMIT 1
) as location
FROM (SELECT p.*,
(SELECT b.id
FROM book b
WHERE b.id_person = p.id
ORDER BY rand()
LIMIT 1
) as book_id
FROM person p
ORDER BY rand()
LIMIT 12
) p INNER JOIN
book b
ON b.id = p.book_id ;
I need to join 2 identical tables to display the same list sorted by id. (posts and posts2)
It happens that before only worked with 1 table, but we've been using a second table (posts2) to store the new data from a certain id.
This is the query I used when I worked with 1 table(posts) and works fine.
select posts.id_usu,posts.id_cat,posts.titulo,posts.html,posts.slug,posts.fecha,hits.id,hits.hits,usuarios.id,usuarios.usuario,posts.id
From posts
Join hits On posts.id = hits.id
Join usuarios On posts.id_usu = usuarios.id
where posts.id_cat='".$catid."' order by posts.id desc
Now I tried to apply this query to Union 2 tables, but I don't know at what point instantiate the JOINS. I tried several ways but sends MYSQL Error. The following query merge the 2 tables and order by id, but need to add the JOIN.
select * from (
SELECT posts.id,posts.id_usu,posts.id_cat,posts.titulo,posts.html,posts.slug,posts.fecha
FROM posts where id_cat='6' ORDER BY id
)X
UNION ALL
SELECT posts2.id,posts2.id_usu,posts2.id_cat,posts2.titulo,posts2.html,posts2.slug,posts2.fecha FROM posts2 where id_cat='4' ORDER BY id DESC limit 20
I need to add this at the above query
Join hits On posts.id = hits.id
Join usuarios On posts.id_usu = usuarios.id
Thanks in advance guys.
If you want the same query as your first query but this time with union of your identical table i.e post2 then you can do so
select
p.id_usu,p.id_cat,p.titulo,p.html,p.slug,p.fecha
,hits.id,hits.hits,usuarios.id,usuarios.usuario
from (
(select
id_usu,id_cat,titulo,html,slug,fecha ,id
From posts
where id_cat='".$catid."' order by id desc limit 20)
UNION ALL
(select
id_usu,id_cat,titulo,html,slug,fecha ,id
From posts2
where id_cat='".$catid."' order by id desc limit 20)
) p
Join hits On p.id = hits.id
Join usuarios On p.id_usu = usuarios.id
order by p.id desc limit 20
Context:
I have an app that shows posts and comments on the home page.
My intention is to limit the number of posts shown (ie, 10 posts) and...
Limit the number of comments shown per post (ie, 2 comments).
Show the total number of comments in the front end (ie, "read all 10 comments")
MySQL:
(SELECT *
FROM (SELECT *
FROM post
ORDER BY post_timestamp DESC
LIMIT 0, 10) AS p
JOIN user_profiles
ON user_id = p.post_author_id
LEFT JOIN (SELECT *
FROM data
JOIN pts
ON pts_id = pts_id_fk) AS d
ON d.data_id = p.data_id_fk
LEFT JOIN (SELECT *
FROM comment
JOIN user_profiles
ON user_id = comment_author_id
ORDER BY comment_id ASC) AS c
ON p.post_id = c.post_id_fk))
I've failed to insert LIMIT and COUNT in this code to get what I want - any suggestions? - will be glad to post more info if needed.
If I'm understanding you correctly you want no more than 10 posts (and 2 comments) to come back for each unique user in the returned result set.
This is very easy in SQLServer / Oracle / Postgre using a "row_number() PARTITION BY".
Unfortunately there is no such function in MySql. Similar question has been asked here:
ROW_NUMBER() in MySQL
I'm sorry I can't offer a more specific solution for MySql. Definitely further research "row number partition by" equivalents for MySql.
The essence of what this does:
You can add a set of columns that make up a unique set, say user id for example sake (this is the "partition") A "row number" column is then added to each row that matches the partition and starts over when it changes.
This should illustrate:
user_id row_number
1 1
1 2
1 3
2 1
2 2
You can then add an outer query that says: select where row_number <= 10, which can be used in your case to limit to no more than 10 posts. Using the max row_number for that user to determine the "read all 10 comments" part.
Good luck!
This is the skeleton of the query you're looking for:
select * from (
select p1.id from posts p1
join posts p2 on p1.id <= p2.id
group by p1.id
having count(*) <= 3
order by p1.post_timestamp desc
) p left join (
select c1.id, c2.post_id from comments c1
join comments c2 on c1.id <= c2.id and c1.post_id = c2.post_id
group by c1.id
having count(*) <= 2
order by c1.comment_timestamp desc
) c
on p.id = c.post_id
It will get posts ordered by their descending timestamp but only the top 3 of them. That result will be joined with the top 2 comments of each post order by their descending timestamp. Just change the column names and it will work :)
How can I use MySQL to count with a LEFT JOIN?
I have two tables, sometimes the Ratings table does not have ratings for a photo so I thought LEFT JOIN is needed but I also have a COUNT statement..
Photos
id name src
1 car bmw.jpg
2 bike baracuda.jpg
Loves (picid is foreign key with photos id)
id picid ratersip
4 1 81.0.0.0
6 1 84.0.0.0
7 2 81.0.0.0
Here the user can only rate one image with their IP.
I want to combine the two tables in order of the highest rating. New table
Combined
id name src picid
1 car bmw.jpg 1
2 bike baracuda.jpg 2
(bmw is highest rated)
My MySQL code:
SELECT * FROM photos
LEFT JOIN ON photos.id=loves.picid
ORDER BY COUNT (picid);
My PHP Code: (UPDATED AND ADDED - Working Example...)
$sqlcount = "SELECT p . *
FROM `pics` p
LEFT JOIN (
SELECT `loves`.`picid`, count( 1 ) AS piccount
FROM `loves`
GROUP BY `loves`.`picid`
)l ON p.`id` = l.`picid`
ORDER BY coalesce( l.piccount, 0 ) DESC";
$pics = mysql_query($sqlcount);
MySQL allows you to group by just the id column:
select
p.*
from
photos p
left join loves l on
p.id = l.picid
group by
p.id
order by
count(l.picid)
That being said, I know MySQL is really bad at group by, so you can try putting the loves count in a subquery in your join to optimize it:
select
p.*
from
photos p
left join (select picid, count(1) as piccount from loves group by picid) l on
p.id = l.picid
order by
coalesce(l.piccount, 0)
I don't have a MySQL instance to test out which is faster, so test them both.
You need to use subqueries:
SELECT id, name, src FROM (
SELECT photos.id, photos.name, photos.src, count(*) as the_count
FROM photos
LEFT JOIN ON photos.id=loves.picid
GROUP BY photos.id
) t
ORDER BY the_count
select
p.ID,
p.name,
p.src,
PreSum.LoveCount
from
Photos p
left join ( select L.picid,
count(*) as LoveCount
from
Loves L
group by
L.PicID ) PreSum
on p.id = PreSum.PicID
order by
PreSum.LoveCount DESC
I believe you just need to join the data and do a count(*) in your select. Make sure you specify which table you want to use for ambigous columns. Also, don't forget to use a group by function when you do a count(*). Here is an example query that I run on MS SQL.
Select CmsAgentInfo.LOGID, LOGNAME, hCmsAgent.SOURCEID, count(*) as COUNT from hCmsAgent
LEFT JOIN CmsAgentInfo on hCmsAgent.logid=CmsAgentInfo.logid
where SPLIT = '990'
GROUP BY CmsAgentInfo.LOGID, LOGNAME, hCmsAgent.SOURCEID
The example results form this will be something like this.
77615 SMITH, JANE 1 36
29422 DOE, JOHN 1 648
Hope that helps. Good Luck.