I have this structure in MySql
I am trying to get:
FIRST post, from LAST topic WHERE category is 'News'
In this example it is row from post where id = 2 as marked on image
So far I got this query:
SELECT *
FROM forum_post AS p
LEFT JOIN forum_topic AS t ON p.topic_id = t.id
LEFT JOIN forum_category AS c ON t.category_id = c.id
WHERE c.title = 'News' AND t.id = MAX(t.id)
ORDER BY p.id ASC LIMIT 1
EDIT:
Dirty solution:
SELECT * FROM forum_post
WHERE topic_id = (SELECT MAX(id) FROM forum_topic WHERE category_id = 1)
ORDER BY id ASC LIMIT 1
You can still use a joined query instead of a subquery to get the first post from last topic of your category,note the subquery in join will run only once to get the result set and in your case subquery will run for each iteration
SELECT * FROM
forum_post AS p
JOIN
(SELECT
t.id
FROM
forum_topic AS t
JOIN forum_category AS c
ON t.category_id = c.id
WHERE c.title = 'News'
ORDER BY t.id DESC
LIMIT 1) t
ON p.topic_id = t.id
ORDER BY p.id ASC
LIMIT 1
select fp.* from forum_post fp,
(select min(fp.id) from forum_post fp where topic_id in
(select max(ft.id) from forum_topic ft inner join forum_category fc
on fc.id = ft.category_id where fc.title = 'News'))T
where fp.id = T.id
[In case there are no forum_posts, no row will be returned]
Edit:
Updated [Although I haven't tried executing it]
I haven't test it, but it shoud be something like this:
SELECT fm.remply
FROM forum_topic ft
JOIN forum_category fc
ON ft.category_id = fc.category_id
AND fc.title = 'News'
JOIN forum_post fm
ON ft.id = fm.topic_id
ORDER BY ft.id DESC
,fm.id DESC
LIMIT 1
Related
I have a select to get alerts.
select 'comments' prefix, c.foto, c.data as data, c.user, concat(k.user, ' comments your post') as logs from comentarios c
inner join posts p on c.foto = p.id
inner join cadastro k on c.user = k.id
where p.user = 1 and p.user <> c.user and c.delete = 0
union all
select 'like' prefix, l.post, l.data as data, l.user, concat(k.user, ' liked your post') as logs from likes l
inner join posts p on l.post = p.id
inner join cadastro k on l.user = k.id
where p.user = 1 and l.user <> p.user
order by data desc
limit 5
The problem is if I run the select this way it will take 2.4871 seconds.
If I remove the select 'like'... = 0.0024, but if I run this select apart it will take only 0.010 without the order by data desc.
any ideas why? I don't know if the problem is the union or the order by...
they are all well indexed.
How do i limit inner join to 1 with order by DESC on this part
INNER JOIN comments ON thread.t=comments.comment_id
this is my code https://gist.github.com/anonymous/cf7de8400327b98631d2f6d9b23084b5
look at result output there is the problem on duplicate content because of comments (need to limit 1) #M Khalid Junaid
Do a self join to your comments table to pick the recent comment only for each post
SELECT
t.t_dp,
t.t,
t.t_id,
t.tittle,
t.t_username,
t.t_date_posting,
t.views,
c.comments,
c.comment_time,
c.comment_id,
c.c
FROM
thread t
INNER JOIN comments c
ON t.t = c.comment_id
LEFT JOIN comments c1
ON c.comment_id = c1.comment_id
AND c.id < c1.id
WHERE t.t_type = '02'
AND c1.id IS NULL
LIMIT #start_from, #results_per_page
Also you are using LIMIT without ORDER BY which makes no sense, In which order limit applies on records.
I don't know much about query optimization but I know the order in which queries get executed
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause
This the query I had written
SELECT
`main_table`.forum_id,
my_topics.topic_id,
(
SELECT MAX(my_posts.post_id) FROM my_posts WHERE my_topics.topic_id = my_posts.topic_id
) AS `maxpostid`,
(
SELECT my_posts.admin_user_id FROM my_posts WHERE my_topics.topic_id = my_posts.topic_id ORDER BY my_posts.post_id DESC LIMIT 1
) AS `admin_user_id`,
(
SELECT my_posts.user_id FROM my_posts WHERE my_topics.topic_id = my_posts.topic_id ORDER BY my_posts.post_id DESC LIMIT 1
) AS `user_id`,
(
SELECT COUNT(my_topics.topic_id) FROM my_topics WHERE my_topics.forum_id = main_table.forum_id ORDER BY my_topics.forum_id DESC LIMIT 1
) AS `topicscount`,
(
SELECT COUNT(my_posts.post_id) FROM my_posts WHERE my_topics.topic_id = my_posts.topic_id ORDER BY my_topics.topic_id DESC LIMIT 1
) AS `postcount`,
(
SELECT CONCAT(admin_user.firstname,' ',admin_user.lastname) FROM admin_user INNER JOIN my_posts ON my_posts.admin_user_id = admin_user.user_id WHERE my_posts.post_id = maxpostid ORDER BY my_posts.post_id DESC LIMIT 1
) AS `adminname`,
(
SELECT forum_user.nick_name FROM forum_user INNER JOIN my_posts ON my_posts.user_id = forum_user.user_id WHERE my_posts.post_id = maxpostid ORDER BY my_posts.post_id DESC LIMIT 1
) AS `nickname`,
(
SELECT CONCAT(ce1.value,' ',ce2.value) AS fullname FROM my_posts INNER JOIN customer_entity_varchar AS ce1 ON ce1.entity_id = my_posts.user_id INNER JOIN customer_entity_varchar AS ce2 ON ce2.entity_id=my_posts.user_id WHERE (ce1.attribute_id = 1) AND (ce2.attribute_id = 2) AND my_posts.post_id = maxpostid ORDER BY my_posts.post_id DESC LIMIT 1
) AS `fullname`
FROM `my_forums` AS `main_table`
LEFT JOIN `my_topics` ON main_table.forum_id = my_topics.forum_id
WHERE (forum_status = '1')
And now I want to know if there is any way to optimize it ? Because all the logic is written in Select section not From, but I don't know how to write the same logic in From section of the query ?
Does it make any difference or both are same ?
Thanks
Correlated subqueries should really be a last resort, they often end up being executed RBAR, and given that a number of your subqueries are very similar, trying to get the same result using joins is going to result in a lot less table scans.
The first thing I note is that all of your subqueries include the table my_posts, and most contain ORDER BY my_posts.post_id DESC LIMIT 1, those that don't have a count with no group by so the order and limit are redundant anyway, so my first step would be to join to my_posts:
SELECT *
FROM my_forums AS f
LEFT JOIN my_topics AS t
ON f.forum_id = t.forum_id
LEFT JOIN
( SELECT topic_id, MAX(post_id) AS post_id
FROM my_posts
GROUP BY topic_id
) AS Maxp
ON Maxp.topic_id = t.topic_id
LEFT JOIN my_posts AS p
ON p.post_id = Maxp.post_id
WHERE forum_status = '1';
Here the subquery just ensures you get the latest post per topic_id. I have shortened your table aliases here for my convenience, I am not sure why you would use a table alias that is longer than the actual table name?
Now you have the bulk of your query you can start adding in your columns, in order to get the post count, I have added a count to the subquery Maxp, I have also had to add a few more joins to get some of the detail out, such as names:
SELECT f.forum_id,
t.topic_id,
p.post_id AS `maxpostid`,
p.admin_user_id,
p.user_id,
t2.topicscount,
maxp.postcount,
CONCAT(au.firstname,' ',au.lastname) AS adminname,
fu.nick_name AS nickname
CONCAT(ce1.value,' ',ce2.value) AS fullname
FROM my_forums AS f
LEFT JOIN my_topics AS t
ON f.forum_id = t.forum_id
LEFT JOIN
( SELECT topic_id,
MAX(post_id) AS post_id,
COUNT(*) AS postcount
FROM my_posts
GROUP BY topic_id
) AS Maxp
ON Maxp.topic_id = t.topic_id
LEFT JOIN my_posts AS p
ON p.post_id = Maxp.post_id
LEFT JOIN admin_user AS au
ON au.admin_user_id = p.admin_user_id
LEFT JOIN forum_user AS fu
ON fu.user_id = p.user_id
LEFT JOIN customer_entity_varchar AS ce1
ON ce1.entity_id = p.user_id
AND ce1.attribute_id = 1
LEFT JOIN customer_entity_varchar AS ce2
ON ce2.entity_id = p.user_id
AND ce2.attribute_id = 2
LEFT JOIN
( SELECT forum_id, COUNT(*) AS topicscount
FROM my_topics
GROUP BY forum_id
) AS t2
ON t2.forum_id = f.forum_id
WHERE forum_status = '1';
I am not familiar with your schema so the above may need some tweaking, but the principal remains - use JOINs over sub-selects.
The next stage of optimisation I would do is to get rid of your customer_entity_varchar table, or at least stop using it to store things as basic as first name and last name. The Entity-Attribute-Value model is an SQL antipattern, if you added two columns, FirstName and LastName to your forum_user table you would immediately lose two joins from your query. I won't get too involved in the EAV vs Relational debate as this has been extensively discussed a number of times, and I have nothing more to add.
The final stage would be to add appropriate indexes, you are in the best decision to decide what is appropriate, I'd suggest you probably want indexes on at least the foreign keys in each table, possibly more.
EDIT
To get one row per forum_id you would need to use the following:
SELECT f.forum_id,
t.topic_id,
p.post_id AS `maxpostid`,
p.admin_user_id,
p.user_id,
MaxT.topicscount,
maxp.postcount,
CONCAT(au.firstname,' ',au.lastname) AS adminname,
fu.nick_name AS nickname
CONCAT(ce1.value,' ',ce2.value) AS fullname
FROM my_forums AS f
LEFT JOIN
( SELECT t.forum_id,
COUNT(DISTINCT t.topic_id) AS topicscount,
COUNT(*) AS postCount,
MAX(t.topic_ID) AS topic_id
FROM my_topics AS t
INNER JOIN my_posts AS p
ON p.topic_id = p.topic_id
GROUP BY t.forum_id
) AS MaxT
ON MaxT.forum_id = f.forum_id
LEFT JOIN my_topics AS t
ON t.topic_ID = Maxt.topic_ID
LEFT JOIN
( SELECT topic_id, MAX(post_id) AS post_id
FROM my_posts
GROUP BY topic_id
) AS Maxp
ON Maxp.topic_id = t.topic_id
LEFT JOIN my_posts AS p
ON p.post_id = Maxp.post_id
LEFT JOIN admin_user AS au
ON au.admin_user_id = p.admin_user_id
LEFT JOIN forum_user AS fu
ON fu.user_id = p.user_id
LEFT JOIN customer_entity_varchar AS ce1
ON ce1.entity_id = p.user_id
AND ce1.attribute_id = 1
LEFT JOIN customer_entity_varchar AS ce2
ON ce2.entity_id = p.user_id
AND ce2.attribute_id = 2
WHERE forum_status = '1';
Say I have this query
SELECT ft.*, m.*
FROM forum_topics ft
INNER JOIN members m ON ft.author = m.id
WHERE ft.forum = '$forum'
ORDER BY ft.lastpost DESC
I want to also get a row count in that from the table forum_replies where the id = ft.id.
How could I do that?
Depending on your DB implementation this might work:
SELECT ft.*,
m.*,
( SELECT count(1)
FROM forum_replies fr
WHERE fr.id = ft.id) AS nr_of_replies
FROM forum_topics ft
INNER JOIN members m ON ft.author = m.id
WHERE ft.forum = '$forum'
ORDER BY ft.lastpost DESC
HTH
SELECT ft.*, m.*, fr.ReplyCount
FROM forum_topics ft
INNER JOIN members m ON ft.author = m.id
inner join (
Select Id, Count(*) as ReplyCount
from forum_replys
group by id
) as fr
on ft.Id = fr.Id
WHERE ft.forum = '$forum'
ORDER BY ft.lastpost DESC
$q = "SELECT s.id, s.title, s.description,
(SELECT COUNT(*) FROM ".FORUM_THREADS." t WHERE t.cat_id = s.id) AS topics,
(SELECT COUNT(*) FROM ".FORUM_REPLIES." r INNER JOIN ".FORUM_THREADS." t ON r.thread_id = t.id
WHERE t.cat_id = s.id) AS replies,
(SELECT r.date FROM ".FORUM_REPLIES." r INNER JOIN ".FORUM_THREADS." t ON r.thread_id = t.id
WHERE t.cat_id = s.id ORDER BY r.date DESC LIMIT 1) AS last_post
FROM ".FORUM_SUBCATEGORIES." s WHERE s.parent = '$catid' AND s.status = '0' ORDER BY s.id";
I am attempting to select more than one field on the following part of the query
(SELECT r.date FROM ".FORUM_REPLIES." r INNER JOIN ".FORUM_THREADS." t ON r.thread_id = t.id
INNER JOIN ".TBL_USERS." u ON u.id = r.author WHERE t.cat_id = s.id ORDER BY r.date DESC LIMIT 1) AS last_post
Along with r.date, I want to select u.username and r.author.
How can I go about doing this?
Thanks!
Just add them to the SELECT:
(SELECT r.date, r.author, u.username FROM ".FORUM_REPLIES." r INNER JOIN ".FORUM_THREADS." t ON r.thread_id = t.id
INNER JOIN ".TBL_USERS." u ON u.id = r.author WHERE t.cat_id = s.id ORDER BY r.date DESC LIMIT 1) AS last_post
UPDATED after comment from OP:
You need to do 3 separate selects OR (depending on your data model) change the query so that the last_post query ends up after/in the FROM clause (there it can have as many columns as you want)...
Luke, you have a central select statement which uses nested select statements for getting the count. You can't depend on the nested select statements to count as the inner join, so you're going to have to add them to the central select statement instead.
In other words, join ".FORUM_REPLIES." and "u" (not sure what that's supposed to represent) with ".FORUM_SUBCATEGORIES.". I'd write the query for you, but I don't know how to link subcategories with replies and subcategories with u.