I've tried about a dozen different methods to solve this issue, and everything I try is breaking my query... I have the following code that is used to generate a loop of threads on a message board:
SELECT MB_TOPICS.*, MAX(MB_REPLIES.TIMESTAMP) AS LATEST
FROM MB_TOPICS
LEFT JOIN MB_REPLIES
ON MB_TOPICS.TOPIC_ID = MB_REPLIES.TOPIC_ID
WHERE MB_TOPICS.CATEGORY_ID='$CATEGORY'
GROUP BY MB_TOPICS.TOPIC_ID
ORDER BY MB_TOPICS.STICKY DESC, LATEST DESC, MB_TOPICS.TIMESTAMP DESC
LIMIT $start,$limit";
This is basically pulling all of the topics within the category, and then via a join it is also getting a timestamp of the most recent reply (if any) from the replies table.
On the sort, I want to keep the most recently active threads at the top... currently (after sticky Y/N) it's sorting by most recent reply and then by the timestamp when the thread was created... this is wrong because it means a new thread will appear after an old thread with replies. I've tried things like
GREATEST(LATEST, MB_TOPICS.TIMESTAMP)
or using IIF statements, CASE statements within the ORDER BY, etc., but anything I do is just breaking the query so that no results appear. I just want to make this so that whichever timestamp is most recent (last reply or topic creation), it sorts descending on that largest value. I know this must be simple but it's killing me today. Thank you!
Edit: If it's helpful information here... the 'LATEST' column will be null for threads that have no replies...
OK, I finally got it. I had to use the MAX() function again rather than the alias, and coalesce to deal with the null values, combined with RiggsFolly's suggestion of pulling it as a new column, resulted in this functioning query:
"SELECT MB_TOPICS.*, MAX(MB_REPLIES.TIMESTAMP) AS LATEST,
GREATEST(COALESCE(MAX(MB_REPLIES.TIMESTAMP),0), MB_TOPICS.TIMESTAMP) AS SORT_ORDER
FROM MB_TOPICS
LEFT JOIN MB_REPLIES ON MB_TOPICS.TOPIC_ID = MB_REPLIES.TOPIC_ID
WHERE MB_TOPICS.CATEGORY_ID='$CATEGORY'
GROUP BY MB_TOPICS.TOPIC_ID
ORDER BY MB_TOPICS.STICKY DESC, SORT_ORDER DESC
LIMIT $start,$limit";
Thanks, I wouldn't have gotten there without the discussion here.
Related
UPDATE:
In the following question, I thought when you select rows, MySQL create a kind of row index, and then the LIMIT and OFFSET clause cuts off this list by its numbers. The problem is I'm using wrong values or field combination to sort the rows as the have almost the same value.
Here is my mistake, assuming to much "intelligence" form MySQL ;-)
The solution is always to have a more reliable sorting field as a fallback, like the ID, like so ORDER BY priority DESC, id ASC
This is a strict MySQL question. Why does it seem the LIMIT OFFSET clause is applied before the ORDER BY? or what am I missing?
Here is the example, first we select a list of rows ordered by a field called priority:
SELECT d0_.name, d0_.id AS id_0, d0_.priority AS priority_1 FROM destination d0_ WHERE d0_.active = 1 ORDER BY d0_.priority DESC;
The results looks like this:
Then I want to select the first 10 rows from this list using the following query:
SELECT d0_.name, d0_.id AS id_0, d0_.priority AS priority_1 FROM destination d0_ WHERE d0_.active = 1 ORDER BY d0_.priority DESC LIMIT 10 OFFSET 10;
And I've got this result:
Why does not the list goes from "Grandvalira" to "Sierra nevada"?
The problem of this, is not the actual order but some rows are never reached! like "Vallnord Ordino-Arcalís". As I change the OFFSET value, it does not go through all the rows, and it event repeats some rows.
This is the basic question. But this is giving me problems at the end when using the "KnpPaginatorBundle (2.5.3)" of Symfony. I thought was a problem of the php code, but mysql queries are giving this unexpected results for me.
Any help or clue of whats going on?
Thanks!
You are not getting the results you are expecting because your data has many rows with the same value for priority.
When you use 'order by' on priority, all the rows with priority can come in any order. There is no guarantee about the ordering with the same value of priority. To resolve the tie, you can add additional fields to your order by clause. Depending on your choice you might choose to include name or id field in the 'order by' clause.
I have the following table that stores messages between users:
I need to display a list of all last message for a users (from all users that have had contact with).
You will see to users being 1000000002 & 1000000172 for example. I need to show the last message between them which could be rows 1 to 4 - but would be 4 as last time.
I have tried the query below but its still isn't right:
SELECT sender_userid,receiver_userid,message,message_read,`datetime` FROM messages
WHERE (receiver_userid='1000000172' OR sender_userid='1000000172') AND friendship_status=1 AND receiver_history=1
GROUP BY receiver_userid
ORDER BY `datetime` ASC;
I find the order by doesn't get the most resent - could be because its after the Group By.
Also find it treats the sender_userid & receiver_userid as different rows in the Group By. I'm unsure how to get the most resent out of both.
thankyou so very much
Your GROUP BY should throw you errors, but MySQL just gives you garbage instead :)
You do not even need a group by, you simply want a list of all messages in which user X is involved and you want to sort them, so you have most of the work domn allready:
SELECT *
FROM messages
WHERE (receiver_userid='1000000172' OR sender_userid='1000000172')
AND friendship_status=1 AND receiver_history=1
ORDER BY `datetime` DESC;
Mind that you want to sort descending if you want the most recent ones first!
use DESC instead of ASC. DESC means large one is first.
I have read a few post on this, but not seeming to be able to fix my problem.
I am calling two database queries to populate two array's that run along side by side of each other, but they aren't matching, as the order that they come out is different. I believe i have something to do with the Group By, and this may require a sub query, but again a little lost...
Query 1:
SELECT count(bids_bid.total_bid), bidtime_bid, users_usr.company_usr, users_usr.id_usr
FROM bids_bid
INNER JOIN users_usr
ON bids_bid.user_bid = users_usr.id_usr
WHERE auction_bid = 36
GROUP BY user_bid
ORDER BY bidtime_bid ASC
Query 2:
SELECT auction_bid, user_bid, bidtime_bid, bids_bid.total_bid
FROM bids_bid
WHERE auction_bid = 36
ORDER BY bidtime_bid ASC
Even though the 'Order by' is the same the results aren't matching. The users are coming out in a different sequence.
I hope this makes sense, and thanks in advance.
* Update *
I just wanted to add a bit of clarity on what the output I want is. I need to only show 1 result by one user (user_bid) the second query show all users rows. I only need the first one to show the first row entered for each user. So if I could order before the the group and by min date, that would be ace...
It's to be expected. You're fetching fields that are NOT involved in the grouping, and are not part of an aggregate function. MySQL allows such things, but generally the results of the ungrouped/unaggregated functions can be wonky.
Because MySQL is free to chose WHICH of the potentially multiple 'free' rows to choose for the actual result row, you will get different results. Generally it picks the first-encountered 'free choice' result, but that's not defined/guaranteed.
You use grouping when you want unique results in result set according to some
group id (column name). usually grouping is used with aggregate functions such as
(min, max,count,sum..).
Ordering or inner query is nothing to do with result set, i suggest read some introductory
tutorials about grouping and think/treat Sql as a set based language and most of the set theory is applied on sql you'll be fine.
So I was complicating issues that I didn't need to. The solution I found was before.
SELECT users_usr.company_usr,
users_usr.id_usr,
bids_bid.bidtime_bid, min(bidtime_bid) as minbid FROM bids_bid INNER JOIN users_usr ON bids_bid.user_bid = users_usr.id_usr
WHERE auction_bid = 36
GROUP BY id_usr
ORDER BY minbid ASC
Thanks everyone for making me look (try) harder...
I fail at mysql, and could really do with some help. I don't know what it would be called, and all my attempts at using combinations of DISTINCT and GROUP BY are just not working out.
I have a table of server monitoring data with these columns:
nStatusNumber
Bandwidth
Load
Users
ServerNumber
DiskFree
MemFree
TimeStamp
**nStatusNumber** - A unique number increasing for each entry
**ServerNumber** - A unique number for each server
For the top of my dashboard for this, I need to display the most recent report for each unique server.
// How many servers are we monitoring ?
$nNumServers = mysql_numrows(mysql_query("SELECT DISTINCT(ServerNumber) FROM server_status;"));
// Get our list of servers
$strQuery = "SELECT * FROM server_status ORDER BY nStatusNumber DESC limit ".$nNumServers.";";
And then loop through the results until we hit $nNumServers . This worked at first, until servers started going down/up and the report order got jumbled.
Say theres 20 servers, the most recent 20 results aren't necessarily 1 from each server.
I'm trying to figure this out in a hurry, and failing at it. I've tried all sorts of combinations of DISTINCT and GROUP BY with no luck so far and would appreciate any guidance on what's probably an embarrassingly easy problem that I just can't see the answer to.
Thanks!
PS - Here's an example query that I've been trying, showing the problem I'm having. Check the "nStatusNumber" field, these should be showing the most recent results only for each server - http://pastebin.com/raw.php?i=ngXLRhd6
PPS - Setting max(nStatusNumber) doesn't give accurate results. I don't want some average/sum/median figure, I need the most recent ACTUAL figures reported by each server. Heres more example results for the queries:
http://pastebin.com/raw.php?i=eyuPD7vj
For your purpose you need to find the row unique to a nServerNumber and TimeStamp. This is not as simple as just saying MAX(TimeStamp) as you need to find the row corresponding to it.
Although I am not an expert in SQL you can try this and see if it works.
SELECT A.nServerNumber, A.nStatusNumber, A.nVNStatsBandwidth, A.fLoad, A.nUsers,
A.nUsersPaid, A.nServerNumber, A.nFreeDisk, A.nTotalDisk, A.nFreeMemory,
A.nTotalMemory, A.TimeStamp
FROM server_status A
INNER JOIN
(
SELECT nServerNumber, MAX(TimeStamp) as `TimeStamp`
FROM server_status
GROUP BY nServerNumber
) B
ON A.nServerNumber = B.nServerNumber
AND A.TimeStamp = B.TimeStamp
ORDER BY A.nServerNumber ASC;
This query will give you all the servers with their latest info. So if you want the total number of servers just run the mysql_numrows(...) function on this result and if you want the data just iterate through the same result (no need to fire two separate SQL queries).
Try this ::
Select
Select MAX(nStatusNumber) from table,
Bandwidth,
Load,
Users,
ServerNumber,
DiskFree,
MemFree,
MAX(`TimeStamp`)
from your table
group by ServerNumber
I am currently building a simple PHP + MySQL forum but I am having problems with getting the information to show in the correct format.
My current SQL code is
SELECT forum_posts.catId, forum_posts.postId, forum_posts.date, forum_posts.message,
forum_posts.userId, users.userId, users.username, forum_thread.threadId, forum_thread.subjectTitle
FROM forum_posts
LEFT JOIN forum_thread ON forum_posts.threadId = forum_thread.threadId
LEFT JOIN users ON users.userId = forum_posts.userId
GROUP BY forum_posts.catId
ORDER BY forum_posts.postId DESC, forum_posts.date DESC, forum_posts.catId ASC
The problem I have is that it brings back everything in the right category but it brings back the first result of the category and not the last one.
I simply want the code to show the last reply in each category.
Any help is much appreciated thank you.
Your query should return a range of rows. Try to limit the result to 1 element. If you sort the results descending, you will get the last item.
ORDER BY ... DESC LIMIT 1
I am not sure whether you find the latest entry by postId or date. If you find it by date, you must start the grouping with the date.
But I don't understand why you are sorting the results so much for getting only one dataset.
ORDER BY forum_posts.date DESC LIMIT 1;
Is this what you want? Additionally this could help you: Select last row in MySQL.