SQL Query:
SELECT
T.*,
U.nick AS author_nick,
P.id AS post_id,
P.name AS post_name,
P.author AS post_author_id,
P.date AS post_date,
U2.nick AS post_author
FROM
zero_topics T
LEFT JOIN
zero_posts P
ON
T.id = P.topic_id
LEFT JOIN
zero_players U
ON
T.author = U.uuid
LEFT JOIN
zero_players U2
ON
P.author = U2.uuid
ORDER BY
CASE
WHEN P.date is null THEN T.date
ELSE P.date
END DESC
Output:
Topics:
Posts:
Question: Why i have duplicated topic id 22? i have in mysql two topics (id 22 and 23) and two posts(id 24 and 25). I want to see topic with last post only.
If a join produces multiple results and you want only at most one result, you have to rewrite the join and/or filtering criteria to provide that result. If you want only the latest result of all the results, it's doable and reasonably easy once you use it a few times.
select a.Data, b.Data
from Table1 a
left join Table2 b
on b.JoinValue = a.JoinValue
and b.DateField =(
select Max( DateField )
from Table2
where JoinValue = b.JoinValue );
The correlated subquery pulls out the one date that is the highest (most recent) value of all the joinable candidates. That then becomes the row that takes part in the join -- or, of course, nothing if there are no candidates at all. This is a pattern I use quite a lot.
Related
I'm currently creating a small application where users can post a text which can be commented and the post can also be voted (+1 or -1).
This is my database:
Now I want to select all information of all posts with status = 1 plus two extra columns: One column containing the count of comments and one column containing the sum (I call it score) of all votes.
I currently use the following query, which correctly adds the count of the comments:
SELECT *, COUNT(comments.fk_commented_post) as comments
FROM posts
LEFT JOIN comments
ON posts.id_post = comments.fk_commented_post
AND comments.status = 1
WHERE posts.status = 1
GROUP BY posts.id_post
Then I tried to additionally add the sum of the votes, using the following query:
SELECT *, COUNT(comments.fk_commented_post) as comments, SUM(votes_posts.type) as score
FROM posts
LEFT JOIN comments
ON posts.id_post = comments.fk_commented_post
AND comments.status = 1
LEFT JOIN votes_posts
ON posts.id_post = votes_posts.fk_voted_post
WHERE posts.status = 1
GROUP BY posts.id_post
The result is no longer correct for either the votes or the comments. Somehow some of the values seem to be getting multiplied...
This is probably simpler using correlated subqueries:
select p.*,
(select count(*)
from comments c
where c.fk_commented_post = p.id_post and c.status = 1
) as num_comments,
(select sum(vp.type)
from votes_posts vp
where c.fk_voted_post = p.id_post
) as num_score
from posts p
where p.status = 1;
The problem with join is that the counts get messed up because the two other tables are not related to each tother -- so you get a Cartesian product.
You want to join comments counts and votes counts to the posts. So, aggregate to get the counts, then join.
select
p.*,
coalesce(c.cnt, 0) as comments,
coalesce(v.cnt, 0) as votes
from posts p
left join
(
select fk_commented_post as id_post, count(*) as cnt
from comments
where status = 1
group by fk_commented_post
) c on c.id_post = p.id_post
left join
(
select fk_voted_post as id_post, count(*) as cnt
from votes_posts
group by fk_voted_post
) v on v.id_post = p.id_post
where p.status = 1
order by p.id_post;
I have this query
SELECT
s.account_number,
a.id AS 'ASPIRION ID',
a.patient_first_name,
a.patient_last_name,
s.admission_date,
s.total_charge,
astat.name AS 'STATUS',
astat.definition,
latest_note.content AS 'LAST NOTE',
a.insurance_company
FROM
accounts a
INNER JOIN
services s ON a.id = s.account_id
INNER JOIN
facilities f ON f.id = a.facility_id
INNER JOIN
account_statuses astat ON astat.id = a.account_status_id
INNER JOIN
(SELECT
account_id, MAX(content) content, MAX(created)
FROM
notes
GROUP BY account_id) latest_note ON latest_note.account_id = a.id
WHERE
a.facility_id = 56
My problem comes from
(SELECT
account_id, MAX(content) content, MAX(created)
FROM
notes
GROUP BY account_id)
Content is a varchar field and I am needed to get the most recent record. I now understand that MAX will not work on a varchar field the way that I want it. I am not sure how to be able to get the corresponding content with the MAX id and group that by account id on in this join.
What would be the best way to do this?
My notes table looks like this...
id account_id content created
1 1 This is a test 2011-03-16 02:06:40
2 1 More test 2012-03-16 02:06:40
Here are two choices. If your content is not very long and don't have funky characters, you can use the substring_index()/group_concat() trick:
(SELECT account_id,
SUBSTRING_INDEX(GROUP_CONCAT(content ORDER BY created desc SEPARATOR '|'
), 1, '|') as content
FROM notes
GROUP BY account_id
) latest_note
ON latest_note.account_id = a.id
Given the names of the columns and tables, that is likely not to work. Then you need an additional join or a correlated subquery in the from clause. I think that might be easiest in this case:
select . . .,
(select n.content
from notes n
where n.account_id = a.id
order by created desc
limit 1
) as latest_note
from . . .
The advantage to this method is that it only gets the notes for the rows you need. And, you don't need a left join to keep all the rows. For performance, you want an index on notes(account_id, created).
SELECT
s.account_number,
a.id AS 'ASPIRION ID',
a.patient_first_name,
a.patient_last_name,
s.admission_date,
s.total_charge,
astat.name AS 'STATUS',
astat.definition,
latest_note.content AS 'LAST NOTE',
a.insurance_company
FROM
accounts a
INNER JOIN services s ON a.id = s.account_id
INNER JOIN facilities f ON f.id = a.facility_id
INNER JOIN account_statuses astat ON astat.id = a.account_status_id
INNER JOIN
(SELECT account_id, MAX(created) mxcreated
FROM notes GROUP BY account_id) latest_note ON latest_note.account_id = a.id and
latest_note.mxcreated = --datetime column from any of the other tables being used
WHERE a.facility_id = 56
You have to join on the max(created) which would give the latest content.
Or you can change the query to
SELECT account_id, content, MAX(created) mxcreated
FROM notes GROUP BY account_id
as mysql allows you even if you don't include all non-aggregated columns in group by clause. However, unless you join on the max date you wouldn't get the correct results.
The last created record is the one for which does not exist a newer one. Hence:
SELECT
s.account_number,
a.id AS "ASPIRION ID",
a.patient_first_name,
a.patient_last_name,
s.admission_date,
s.total_charge,
astat.name AS "STATUS",
astat.definition,
latest_note.content AS "LAST NOTE",
a.insurance_company
FROM accounts a
INNER JOIN services s ON a.id = s.account_id
INNER JOIN facilities f ON f.id = a.facility_id
INNER JOIN account_statuses astat ON astat.id = a.account_status_id
INNER JOIN
(
SELECT account_id, content
FROM notes
WHERE NOT EXISTS
(
SELECT *
FROM notes newer
WHERE newer.account_id = notes.account_id
AND newer.created > notes.created
)
) latest_note ON latest_note.account_id = a.id
WHERE a.facility_id = 56;
I have three tables, libraryitems, copies and loans.
A libraryitem hasMany copies, and a copy hasMany loans.
I'm trying to get the latest loan entry for a copy only; The query below returns all loans for a given copy.
SELECT
libraryitems.title,
copies.id,
copies.qruuid,
loans.id AS loanid,
loans.status,
loans.byname,
loans.byemail,
loans.createdAt
FROM copies
INNER JOIN libraryitems ON copies.libraryitemid = libraryitems.id AND libraryitems.deletedAt IS NULL
LEFT OUTER JOIN loans ON copies.id = loans.copyid
WHERE copies.libraryitemid = 1
ORDER BY copies.id ASC, loans.createdAt DESC
I know there needs to be a sub select of some description in here, but struggling to get the correct syntax. How do I only return the latest, i.e MAX(loans.createdAt) row for each distinct copy? Just using group by copies.id returns the earliest, rather than latest entry.
Image example below:
in the subquery , getting maximum created time for a loan i.e. latest entry and joining back with loans to get other details.
SELECT
T.title,
T.id,
T.qruuid,
loans.id AS loanid,
loans.status,
loans.byname,
loans.byemail,
loans.createdAt
FROM
(
SELECT C.id, C.qruuid, L.title, MAX(LN.createdAt) as maxCreatedTime
FROM Copies C
INNER JOIN libraryitems L ON C.libraryitemid = L.id
AND L.deletedAt IS NULL
LEFT OUTER JOIN loans LN ON C.id = LN.copyid
GROUP BY C.id, C.qruuid, L.title) T
JOIN loans ON T.id = loans.copyid
AND T.maxCreatedTime = loans.createdAt
A self left join on loans table will give you latest loan of a copy, you may join the query to the other tables to fetch the desired output.
select * from loans A
left outer join loans B
on A.copyid = B.copyid and A.createdAt < B.createdAt
where B.createdAt is null;
This is your query with one simple modification -- table aliases to make it clearer.
SELECT li.title, c.id, c.qruuid,
l.id AS loanid, l.status, l.byname, l.byemail, l.createdAt
FROM copies c INNER JOIN
libraryitems li
ON c.libraryitemid = li.id AND
li.deletedAt IS NULL LEFT JOIN
loans l
ON c.id = l.copyid
WHERE c.libraryitemid = 1
ORDER BY c.id ASC, l.createdAt DESC ;
With this as a beginning let's think about what you need. You want the load with the latest createdAt date for each c.id. You can get this information with a subquery:
select l.copyid, max(createdAt)
from loans
group by l.copyId
Now, you just need to join this information back in:
SELECT li.title, c.id, c.qruuid,
l.id AS loanid, l.status, l.byname, l.byemail, l.createdAt
FROM copies c INNER JOIN
libraryitems li
ON c.libraryitemid = li.id AND
li.deletedAt IS NULL LEFT JOIN
loans l
ON c.id = l.copyid LEFT JOIN
(SELECT l.copyid, max(l.createdAt) as maxca
FROM loans
GROUP BY l.copyid
) lmax
ON l.copyId = lmax.copyId and l.createdAt = lmax.maxca
WHERE c.libraryitemid = 1
ORDER BY c.id ASC, l.createdAt DESC ;
This should give you the most recent record. And, the use of left join should keep all copies, even those that have never been leant.
I have this query (below) while it does work I am wondering if it is the best as it will be going against thousands of records. I will try to explain the best I can.
SELECT items.*,
p.file AS item_pic,
i_f.id AS favorite_id,
COALESCE(f.favorite_count, 0) AS favorite_count,
COALESCE(b.num_buys, 0) AS num_buys,
COALESCE(c.comment_count, 0) AS comment_count
FROM items i
INNER JOIN (SELECT file,
item_id
FROM item_pics
ORDER BY item_pics.id ASC) AS p
ON p.item_id = i.id
LEFT JOIN (SELECT COUNT(*) AS favorite_count,
item_id
FROM item_favorites
GROUP BY item_id) AS f
ON f.item_id = i.id
LEFT JOIN (SELECT COUNT(*) AS num_buys,
item_id
FROM purchases
GROUP BY item_id) AS b
ON b.item_id = i.id
LEFT JOIN (SELECT COUNT(*) AS comment_count,
item_id
FROM comments
GROUP BY item_id) AS c
ON c.item_id = i.id
LEFT JOIN item_favorites AS i_f
ON i.id = i_f.item_id
AND i_f.userid = '14'
GROUP BY i.id
LIMIT 0, 20
So we are selecting the items in the database. The first join is for a picture (Items have multiple pictures but I only want one).
The next join is for favorite count. Each time a user favorites something it adds it to the table favorites with some info, so I am just trying to get the total number of favorites for that item.
Next up is the number of purchases for this item. Pretty much the same as favorites.
After that it is for comments. Again this is just like the purchases and favorites count.
The last join is to see if the logged in user (id 14) has favorited this item if not I use COALESCE to return 0.
Like I said this all works correctly but it does take a few seconds to load on a table of about 6700 items and about 180K rows in the purchases table for only loading 20 at a time (I do a scrolling/load similar to Facebook/Twitter). Indexes have been properly setup on all tables. Once this is complete/correct I would like to know how to limit results for purchases in the last seven days and order by number of purchases (num_buys).
EDIT: Results from EXPLAIN
I suppose you want the first picture (lowest id), and pictures are required, where as everything else is optional.
I guess you're doing subqueries because you think joining on uncorrelated subqueries (hitting the joined tables just once) will be faster than correlated subqueries or a plain JOIN. However, you end up having to lookup the records twice, and the second lookup (for the actual join) doesn't get to use an index because derived (temporary tables) don't have indexes.
Try normal JOINs:
SELECT items.*,
p.file AS item_pic,
COALESCE(i_f.id, 0) AS favorite_id,
COUNT(f.item_id) AS favorite_count,
COUNT(b.item_id) AS num_buys,
COUNT(c.item_id) AS comment_count
FROM items i
STRAIGHT_JOIN item_pics p
ON p.item_id = i.id
LEFT JOIN item_pics p2
ON p2.item_id = i.id
AND p2.id < p1.id
LEFT JOIN item_favorites f
ON f.item_id = i.id
LEFT JOIN purchases b
ON b.item_id = i.id
LEFT JOIN comments c
ON c.item_id = i.id
LEFT JOIN item_favorites AS i_f
ON i_f.item_id = i.id
AND i_f.userid = '14'
WHERE p2.id IS NULL
GROUP BY i.id
LIMIT 20
The double join on pictures is an anti-join WHERE p2.id IS NULL, to retrieve the picture with the lowest id.
I have 3 tables: activites, taks and requirements. I want to return all of the duration of all the tasks for a specific requirement. This is my query:
SELECT r.id as req_id,
r.project_id,
r.name as req_name,
r.cost,r.estimated,
p.name as project_name,
v.name AS `status` ,
t.taskid,
(SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(duration)))
FROM activities a
WHERE a.taskid = t.taskid) AS worked
FROM requirements r
INNER JOIN projects p
ON p.projectid = r.project_id
INNER JOIN `values` v
ON v.id = r.r_status_id
LEFT JOIN tasks t
on t.id_requirement = r.id
WHERE 1 = 1
ORDER BY req_id desc
And this is the result :
As you can see there are 2 same req_id (48) . I want to appear one time and get the sum of the last two rows in worked. How can I manage that ?
this is the activities structure :
this is tasks structure :
and this is the requirement structure :
Include your activities table in the JOIN, GROUP by all requirement columns you need and add a sum. Since you are aggregating tasks, you cannot have taskid in the SELECT clause.
SELECT r.id as req_id,
r.project_id,
r.name as req_name,
r.cost,r.estimated,
p.name as project_name,
v.name AS `status` ,
SEC_TO_TIME(SUM(TIME_TO_SEC(a.duration)))
FROM requirements r
INNER JOIN projects p ON p.projectid = r.project_id
INNER JOIN `values` v ON v.id = r.r_status_id
LEFT JOIN tasks t ON t.id_requirement = r.id
LEFT JOIN activities a ON a.taskid=t.taskid
WHERE 1 = 1
GROUP BY r.id, r.project_id, r.name,r.cost,r.estimated,p.name, v.name
ORDER BY req_id desc
The joins in your query appear to be creating extra rows. I'm sure there is a way to fix the logic directly, possibly by pre-aggregating some results in the from clause.
Your duplicates appear to be complete duplicates (every column is exactly the same). The easy way to fix the problem is to use select distinct. So, just start your query with:
SELECT DISTINCT r.id as req_id, r.project_id, r.name as req_name,
. . .
I suspect that one of your underlying tables has duplicated rows that you are not expecting, but that is another issue.