I have 3 separate queries at the moment that I'm trying to combine together so it is more efficient.
The reason I'm putting them together is so that I can sort all of the results by submitdate, as of right now they are sorted by submitdate but are separated by each query.
First is
Query that gets all posts that I have commented on that have new comments
SELECT DISTINCT p.*,c.submitdate as MostRecentSubmitDate
FROM posts p
INNER JOIN comments c
ON c.postid = p.id
WHERE c.submitdate > (
SELECT MAX(c2.submitdate)
FROM comments c2
WHERE c2.postid = c.postid
AND c2.deviceID = ?
)
Second is
Query that gets most recent replies on my posts.
SELECT p.PostTitle,p.id AS PostID,c1.id AS CommentID, c1.comment, q.LatestCommentDate, c1.deviceID
FROM (SELECT c.postid, MAX(c.SubmitDate) AS LatestCommentDate
FROM comments c GROUP BY c.postid) q
INNER JOIN posts p ON q.postid = p.id and ? = p.deviceiD
INNER JOIN comments c1 ON q.LatestCommentDate = c1.submitDate
Third is
Query that gets the amount of votes on each of my posts
SELECT * FROM posts
WHERE DEVICEID = ?
AND PostVotes > 0
ORDER BY SUBMITDATE
You can use UNION to combine all your queries together.
Rules to make a UNION
The number and the order of the columns must be the same in all queries.
The data types must be compatible.
query 1
UNION
query 2
UNION
query 3
ORDER BY ...
Related
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 have three tables projects, discussions, and comments.
I have tried it like this:
SELECT p.PRO_Name, COUNT( d.DIS_Id ) AS nofdisc, COUNT( c.COM_Id ) AS nofcom
FROM projects p
LEFT JOIN discussions d ON p.PRO_Id = d.PRO_Id
LEFT JOIN comments c ON d.DIS_Id = c.DIS_Id
GROUP BY p.PRO_Name LIMIT 0 , 30
But it's taking all the rows from discussions and the count of comments is the same as the count of discussions.
count counts the number of non-null values of the given parameter. The join you have will create a row per comment, where both dis_id and com_id are not null, so their counts would be the same. Since these are IDs, you could just count the distinct number of occurrences to get the response you'd want:
(EDIT: Added an order by clause as per the request in the comments)
SELECT p.PRO_Name,
COUNT(DISTINCT d.DIS_Id) AS nofdisc,
COUNT(DISTINCT c.COM_Id) AS nofcom
FROM projects p
LEFT JOIN discussions d ON p.PRO_Id = d.PRO_Id
LEFT JOIN comments c ON d.DIS_Id = c.DIS_Id
GROUP BY p.PRO_Name
ORDER BY 2,3
LIMIT 0 , 30
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.