This is my table structure in database
I want to get number of likes for each post by counting post field in likes table and display it for every post using foreach loop.
My question is
Is there a way i can do this with one query with JOIN, GROUP BY and COUNT tables and not create multiple queries.
select p.id, p.title, p.content, count(l.id) as likes_count
from posts p
left join likes l on l.post = p.id
group by p.id, p.title, p.content
http://sqlfiddle.com/#!9/bca8ee/1
SELECT p.*, COUNT(l.id)
FROM posts p
LEFT JOIN likes l
ON l.post = p.id
GROUP BY p.id
Related
I am listing the tags/categories on the user's page. I would like to show the number of posts the user made for each tag. The tags, the posts, and the post-tags are in different tables.
The difficulty is, that there are two kind of posts. The posts, and the comments. They are in the same table, but different type. "question" and "answer". the related_id at the answers are the id of the posts they are related to.
I tried to solve in pretty lot of way but couldn't get it to work.
My db structures:
For tags:
tagid tag_name
For posts
id type(enum:"question","answer") related_id user_id
For post-tags:
post_id tag_id
The code what I tried is the following:
$user_active_query = mysql_query("select p.id,
p.user_id,
pt.post_id,
count(pt.post_id),
pt.tag_id,
t.tagid,
t.tag_name
from posts p
inner join post_tags pt
inner join tags t
on p.id = pt.post_id
and pt.tag_id = t.tagid
where p.user_id = '$uid'
group by t.tagid");
while($useractive = mysql_fetch_array($user_active_query)) {
$user_active_counter = $useractive['count(pt.post_id)'];
echo "<a href='' class='btn btn-mini' style='margin:3px;'>".$useractive['tag_name']." (".$user_active_counter.")</a>";
}
User id is given on the page. "$uid". I am just tired of the lot of try and asking for correction. First it seemed to be the best way to store the post-tags but now this is a nightmare. I mean, for me, its seems impossible to do this with this structure.
You can get both counts i.e the no of answers and no of questions posted by a user ,here is the trick also use proper join syntax you are missing the on clause for join
SELECT
p.id,
p.user_id,
pt.post_id,
COUNT(pt.post_id) all_posts,
COALESCE(SUM(`type` = 'question')) questions,
COALESCE(SUM(`type` = 'answer')) answers,
pt.tag_id,
t.tagid,
t.tag_name
FROM tags t
LEFT JOIN post_tags pt ON(pt.tag_id = t.tagid)
LEFT JOIN posts p ON p.id = pt.post_id
WHERE p.user_id = '$uid'
GROUP BY t.tagid
Note in mysql sum with some expression will result in a boolean
Edit from comments add another condition using OR in your last join so first condition will join the posts that are associated with tags ,and as your explanation tags are not directly linked with answers but answer are linked to their question with related id so can join the related id of each answer to tag id so this way can get the tags for answers too
SELECT
p.id,
p.user_id,
pt.post_id,
COUNT(pt.post_id) all_posts,
COALESCE(SUM(`type` = 'question')) questions,
COALESCE(SUM(`type` = 'answer')) answers,
pt.tag_id,
t.tagid,
t.tag_name
FROM tags t
LEFT JOIN post_tags pt ON(pt.tag_id = t.tagid)
LEFT JOIN posts p ON (p.id = pt.post_id OR p.related_id = pt.post_id)
WHERE p.user_id = '$uid'
GROUP BY t.tagid
I think you only need to include p.type in your group by clause
$user_active_query = mysql_query("
select
p.id,
p.user_id,
pt.post_id,
count(pt.post_id),
pt.tag_id,
t.tagid,
t.tag_name
from posts p
inner join post_tags pt
inner join tags t
on p.id = pt.post_id
and pt.tag_id = t.tagid
where p.user_id = '$uid'
group by t.tagid, p.type"
);
so, we will group per type too.
I'm not sure I fully understand your schema design. But it sounds like you have two join "paths", one to get to the question type posts, and another to get to child answer type posts.
To get the count of the question-type posts (by a specific user) related to each tag, looks like what you have so far, basically:
SELECT t.tagid
, t.tag_name
, COUNT(p.id) AS count_question
FROM tags t
JOIN post_tags pt
ON pt.tag_id = t.tagid
JOIN posts p
ON p.id = pt.post_id
AND p.type = 'question'
WHERE p.user_id = '$uid'
GROUP BY t.tagid
To get the count of the answer-type posts (by a specific user) related to a question related to each tag, we first need to join to the 'question' (to get the tags), and then join to the related answer. This is nearly identical to the first query, except that we add another join to posts table to get the "child" answer-type posts (so we can get a count of the answer-type posts), and we are not restricting the question-type posts to those from the specific user... we are going to count the answer-type posts from a user posted against any user's question.
SELECT t.tagid
, t.tag_name
, COUNT(a.id) AS count_answer
FROM tags t
JOIN post_tags pt
ON pt.tag_id = t.tagid
JOIN posts p
ON p.id = pt.post_id
AND p.type = 'question'
JOIN posts a
ON a.related_id = p.id
AND a.type = 'answer'
WHERE a.user_id = '$uid'
GROUP BY t.tagid
If each of those queries returns a portion of the total count you want to return, those can be combined, but it gets a little bit messy.
The most straightforward approach is to combine those two results with a UNION ALL set operator, and then use that as an inline view, i.e. run another query against the combined resultset.
For example:
SELECT r.tagid
, r.tagname
, SUM(r.count_post) AS count_total
, SUM(IF(r.type='q',r.count_post,0)) AS count_question
, SUM(IF(r.type='a',r.count_post,0)) AS count_answer
FROM (
SELECT 'q' AS type
, t.tagid
, t.tag_name
, COUNT(p.id) AS count_post
FROM tags t
JOIN post_tags pt
ON pt.tag_id = t.tagid
JOIN posts p
ON p.id = pt.post_id
AND p.type = 'question'
WHERE p.user_id = '$uid'
GROUP BY t.tagid
UNION ALL
SELECT 'a' AS type
, t.tagid
, t.tag_name
, COUNT(a.id) AS count_post
FROM tags t
JOIN post_tags pt
ON pt.tag_id = t.tagid
JOIN posts p
ON p.id = pt.post_id
AND p.type = 'question'
JOIN posts a
ON a.related_id = p.id
AND a.type = 'answer'
WHERE a.user_id = '$uid'
GROUP BY t.tagid
) r
GROUP BY r.tag_id
If you aren't interested in the individual counts (of question and answer type posts), then just remove those two expressions from the SELECT list of the outer query, and you can also remove the type='q', type='a' discriminator column from the inline view query.
This isn't the only way to combine the results, but I think it's the easiest way to verify we're getting a "correct" result (we can run just the inline view query and verify that the results from that are correct.
Another approach to combining them is messier, and more difficult to decipher.
We basically need to join to question-type posts from all users, and then do an outer join operation to the answer-type posts from the specific user.
We can use predicates in the WHERE clause to filter out the rows, so that return only rows that have a matching answer-type row -OR- are a question-type row poseted by the specified user.
In the SELECT list, we need to do some additional filtering, so that we filter out posts from other users.
Something like this:
SELECT t.tagid
, t.tag_name
, COUNT(DISTINCT IF(p.user_id='$uid',p.id,NULL))
+ COUNT(DISTINCT a.id) AS count_total
, COUNT(DISTINCT IF(p.user_id='$uid',p.id,NULL)) AS count_question
, COUNT(DISTINCT a.id) AS count_question
FROM tags t
JOIN post_tags pt
ON pt.tag_id = t.tagid
JOIN posts p
ON p.id = pt.post_id
AND p.type = 'question'
LEFT
JOIN posts a
ON a.related_id = p.id
AND a.type = 'answer'
AND a.user_id = '$uid'
WHERE p.user_id = '$uid'
OR a.id IS NOT NULL
GROUP BY t.tagid
But, I'd don't really like this query, it's too hard to figure out what's going on. I'd opt for the (previous) query, with the UNION ALL inline view. That's easier to decipher.
I have two tables :
posts : id,title,content,show,created_at
comments: id,post_id,created_at
I'm trying to order posts by most commented.
SELECT *, COUNT(comments.id) AS total_comments
FROM comments LEFT JOIN posts ON posts.id = comments.post_id
WHERE posts.show = '1'
GROUP BY complains.id
ORDER BY total_comments DESC
The problem is that the posts with 0 comments don't appear.
Any help would be much appreciated.
With your join above, you are incorrectly joining to get commens that have posts
You should have done a right join or swap the tables in left join like below.
Select *, COUNT(comments.id) as total_comments
FROM posts
LEFT outer JOIN comments on posts.id = comments.post_id
WHERE posts.show = '1'
GROUP BY posts.id
ORDER BY total_comments DESC
You need to do a RIGHT JOIN instead of a LEFT JOIN. Or swap the tables in the LEFT JOIN clause.
While there are many ways to solve this, I think this code is easy to read and understand.
The query in the LEFT JOIN can be copied out and run on its own to help debug. Then you join that result set to the posts table and order the results.
SELECT p.*, IFNULL(c.total_comments, 0) as total_comments
FROM posts p
LEFT JOIN (select post_id, count(post_id) as total_comments from comments group by post_id) as c ON p.id = c.post_id
WHERE p.show = '1'
ORDER BY c.total_comments DESC
I'm indexing two things of posts. One is the title (words) and two are the keywords. I've chosen to use 3 tables for this:
word_index (word,word_id) // al words and keywords are indexed
keyword_rel (word_id,postId) // relations with the keywords
word_rel (word_id,postId) // relations with the the words of the title
Now I'm trying to perform a decent search query on this. Using the keywords only, it works fine.
SELECT p.postId
FROM word_index wi
INNER JOIN keyword_rel kr ON wi.word_id=kr.word_id
INNER JOIN post p ON p.postId=kr.postId
WHERE wi.word LIKE 'input%'
GROUP BY p.postId
But now I would like to include word_rel to also search in the title.
I tried this, but it doesn't sound right and also doesn't return everything (missing some of wi.word):
SELECT p.postId,wi.word
FROM word_index wi
INNER JOIN keyword_rel kr ON wi.word_id=kr.word_id
INNER JOIN word_rel wr ON wi.word_id = wr.word_id
INNER JOIN post p ON p.postId=kr.postId
INNER JOIN post pi ON pi.postId=wr.postId
WHERE wi.word LIKE 'input%'
GROUP BY p.postId
The problem is with INNER JOIN post p which is related to keyword_rel. Now I also need it related to word_rel. What is a good way to do this ?
You would need to do a UNION here:
SELECT p.postId, wi.word
FROM word_index wi
INNER JOIN keyword_rel kr ON wi.word_id = kr.word_id
INNER JOIN post p ON p.postId=kr.postId
WHERE wi.word LIKE 'input%'
GROUP BY p.postId
UNION
SELECT p.postId, wi.word
FROM word_index wi
INNER JOIN word_rel wr ON wi.word_id = wr.word_id
INNER JOIN post p ON p.postId=wr.postId
WHERE wi.word LIKE 'input%'
GROUP BY p.postId
And since this may return some of the results twice or more times (especially if the word is contained in both keywords and titles), You may want to wrap the above query into another SELECT DISTINCT:
SELECT DISTINCT t.post_id, t.word
FROM (
SELECT ...
UNION
SELECT
) t
ORDER BY t.word ASC
im running a query that usses 3 tabels "post, likes and comment" i need to get the ammount of likes and comments the post has got, and at the same time get the basic info from the post table so im using the query bellow but the problem is that it copys the value likeAmount to commentAmount if likes is bigger unless comments is 0.
SELECT post.*, COUNT(likes.id) as 'LikeAmount', COUNT(comment.id) as 'commentAmount' FROM post
LEFT JOIN likes ON post.id = likes.post
LEFT JOIN comment ON post.id = comment.post
GROUP BY post.id
ORDER BY LikeAmount DESC"
so that doesnt work but when i add distinct it does work, so when its like this:.
SELECT post.*, COUNT(distinct likes.id) as 'LikeAmount', COUNT(distinct comment.id) as 'commentAmount' FROM post
LEFT JOIN likes ON post.id = likes.post
LEFT JOIN comment ON post.id = comment.post
GROUP BY post.id
ORDER BY LikeAmount DESC";
i dont see why it works with distinct and doesnt with out, and does distinct mather performance wise or does it make no diffrence sinds it will be used in a website that has a lott of trafic..
try this, not short, but readable:
SELECT
p.*,
pl.like_count,
pc.comment_count
FROM post p
#join likes
LEFT OUTER JOIN (
SELECT
post,
COUNT(*) AS like_count
FROM likes
GROUP BY post
) AS pl
ON pl.post = p.id
#join comments
LEFT OUTER JOIN (
SELECT
post,
COUNT(*) AS comment_count
FROM comment
GROUP BY post
) AS pc
ON pc.post = p.id
Perhaps using SUM instead of COUNT to handle the records where there is no join would work, and should perform just as fast:
SELECT post.id,
SUM(IF(likes.id IS NULL,0,1)) as 'LikeAmount',
SUM(IF(comment.id IS NULL,0,1)) as 'commentAmount'
FROM post
LEFT JOIN likes ON post.id = likes.post
LEFT JOIN comment ON post.id = comment.post
GROUP BY post.id
ORDER BY LikeAmount DESC"
I'm really sorry for the first post as i didn't explain everything.
Basically i have 3 tables, One for posts, One for Categories, & Another to link categories with posts.
I want in a single MySQL query to select posts that are under a specific category.
posts(id,title,body)
---------------------
125,Some title,Blah blah
categories(id,name)
---------------------
1,politic
2,entertainment
linker(categoryid,postid)
---------------------
2,125
I want in single query to fetch posts in the entertainment category by example, what to do?
Thanks
select
p.*
from
posts p
inner join linker l on l.postid = p.id
inner join categories c on c.categoryid = l.categoryid
where
c.name = 'entertainment'
The following SQL statement should provide you with a basis for what you are trying to do.
select p.*
from posts p
inner join linker l
on l.postid = p.id
inner join categories c
on l.categoryid = c.id
where c.name = 'entertainment'
If a post belongs to 2 categories, you can still use pinkfloydx33's query with DISTINCT in the select statement:
select
DISTINCT p.*
from
posts p
inner join linker l on l.postid = p.id
inner join categories c on c.categoryid = l.categoryid
where
c.name = 'entertainment'
The result set will show only one record.
It's the same exact thing, you just have to join 3 tables intead of 2 :
SELECT P.id post_id,
P.title,
P.body,
C.id category_id,
C.name
FROM posts P
INNER JOIN linker L
ON P.id = L.postid
INNER JOIN categories C
ON L.categoryid = C.id
WHERE C.name = 'Category'
Don't be afraid to do your own tests. If you understand how to join two tables, you should understand how to join three, four and more.
If you are specifying only one category in the WHERE clause, then the result will be a single row for each post ID.
Either way you can use DISTINCT or GROUP BY when the result could be more than one row per ID, but in that case i prefer the second one (GROUP BY).