I have two tables like these:
Table "users":
user_id | source
----------------
1 | 2
2 | 2
3 | 3
4 | 0
Table "sources":
source_id | name
----------------
1 | "one"
2 | "two"
3 | "three"
4 | "four"
Now I need to SELECT (*) FROM source and additionally COUNT "users" that have this source, BUT if there is an additional filter(requests by PHP mysqli), then additionally sort "sources" table by its users count.
What is the best way to do so, and is it possible to do in one statement?
--------------Added editing----------
The first part(SELECT with count from another table) I'm doing this way:
SELECT
id, name
(select count(*) from users where source = sources.id) as sourceUsersCount
FROM sources
And now, how to order this list by users count in each source?
Please check the below query if this is what you need.
select s.*,a.c from sources s
left join
(select count(*) as c,source as src
from user u join sources s
on s.source_id = u.source group by u.source) a
on s.source_id = a.src;
Count the number of users:
SELECT sources.*, COUNT(users.user_id) FROM sources
LEFT JOIN users ON users.source_id = sources.source_id
GROUP BY sources.source_id;
I assume by filters you mean the WHERE clause:
SELECT sources.*, COUNT(users.user_id) FROM sources
LEFT JOIN users ON users.source_id = sources.source_id
WHERE sources.source_id = 2
GROUP BY sources.source_id;
And you can always attach an ORDER BY on the end for sorting:
SELECT sources.*, COUNT(users.user_id) FROM sources
LEFT JOIN users ON users.source_id = sources.source_id
GROUP BY sources.source_id
ORDER BY sources.source_id DESC;
Achieved it by doing so:
SELECT
sources.*,
count(users.source) as sourceUsersCount
FROM sources
LEFT JOIN users ON sources.id = users.source
//In case of additional filters
WHERE
id != 0 AND (name LIKE %?% OR id LIKE %?%)
//\\
GROUP BY sources.id
//In case of sorting by "users" count
ORDER BY sourceUsersCount ASC
//\\
Is it the best way, or maybe there are some faster variants?
I have a table ("lms_attendance") of users' check-in and out times that looks like this:
id user time io (enum)
1 9 1370931202 out
2 9 1370931664 out
3 6 1370932128 out
4 12 1370932128 out
5 12 1370933037 in
I'm trying to create a view of this table that would output only the most recent record per user id, while giving me the "in" or "out" value, so something like:
id user time io
2 9 1370931664 out
3 6 1370932128 out
5 12 1370933037 in
I'm pretty close so far, but I realized that views won't accept subquerys, which is making it a lot harder. The closest query I got was :
select
`lms_attendance`.`id` AS `id`,
`lms_attendance`.`user` AS `user`,
max(`lms_attendance`.`time`) AS `time`,
`lms_attendance`.`io` AS `io`
from `lms_attendance`
group by
`lms_attendance`.`user`,
`lms_attendance`.`io`
But what I get is :
id user time io
3 6 1370932128 out
1 9 1370931664 out
5 12 1370933037 in
4 12 1370932128 out
Which is close, but not perfect. I know that last group by shouldn't be there, but without it, it returns the most recent time, but not with it's relative IO value.
Any ideas?
Thanks!
Query:
SQLFIDDLEExample
SELECT t1.*
FROM lms_attendance t1
WHERE t1.time = (SELECT MAX(t2.time)
FROM lms_attendance t2
WHERE t2.user = t1.user)
Result:
| ID | USER | TIME | IO |
--------------------------------
| 2 | 9 | 1370931664 | out |
| 3 | 6 | 1370932128 | out |
| 5 | 12 | 1370933037 | in |
Note that if a user has multiple records with the same "maximum" time, the query above will return more than one record. If you only want 1 record per user, use the query below:
SQLFIDDLEExample
SELECT t1.*
FROM lms_attendance t1
WHERE t1.id = (SELECT t2.id
FROM lms_attendance t2
WHERE t2.user = t1.user
ORDER BY t2.id DESC
LIMIT 1)
No need to trying reinvent the wheel, as this is common greatest-n-per-group problem. Very nice solution is presented.
I prefer the most simplistic solution (see SQLFiddle, updated Justin's) without subqueries (thus easy to use in views):
SELECT t1.*
FROM lms_attendance AS t1
LEFT OUTER JOIN lms_attendance AS t2
ON t1.user = t2.user
AND (t1.time < t2.time
OR (t1.time = t2.time AND t1.Id < t2.Id))
WHERE t2.user IS NULL
This also works in a case where there are two different records with the same greatest value within the same group - thanks to the trick with (t1.time = t2.time AND t1.Id < t2.Id). All I am doing here is to assure that in case when two records of the same user have same time only one is chosen. Doesn't actually matter if the criteria is Id or something else - basically any criteria that is guaranteed to be unique would make the job here.
Based in #TMS answer, I like it because there's no need for subqueries but I think ommiting the 'OR' part will be sufficient and much simpler to understand and read.
SELECT t1.*
FROM lms_attendance AS t1
LEFT JOIN lms_attendance AS t2
ON t1.user = t2.user
AND t1.time < t2.time
WHERE t2.user IS NULL
if you are not interested in rows with null times you can filter them in the WHERE clause:
SELECT t1.*
FROM lms_attendance AS t1
LEFT JOIN lms_attendance AS t2
ON t1.user = t2.user
AND t1.time < t2.time
WHERE t2.user IS NULL and t1.time IS NOT NULL
Already solved, but just for the record, another approach would be to create two views...
CREATE TABLE lms_attendance
(id int, user int, time int, io varchar(3));
CREATE VIEW latest_all AS
SELECT la.user, max(la.time) time
FROM lms_attendance la
GROUP BY la.user;
CREATE VIEW latest_io AS
SELECT la.*
FROM lms_attendance la
JOIN latest_all lall
ON lall.user = la.user
AND lall.time = la.time;
INSERT INTO lms_attendance
VALUES
(1, 9, 1370931202, 'out'),
(2, 9, 1370931664, 'out'),
(3, 6, 1370932128, 'out'),
(4, 12, 1370932128, 'out'),
(5, 12, 1370933037, 'in');
SELECT * FROM latest_io;
Click here to see it in action at SQL Fiddle
If your on MySQL 8.0 or higher you can use Window functions:
Query:
DBFiddleExample
SELECT DISTINCT
FIRST_VALUE(ID) OVER (PARTITION BY lms_attendance.USER ORDER BY lms_attendance.TIME DESC) AS ID,
FIRST_VALUE(USER) OVER (PARTITION BY lms_attendance.USER ORDER BY lms_attendance.TIME DESC) AS USER,
FIRST_VALUE(TIME) OVER (PARTITION BY lms_attendance.USER ORDER BY lms_attendance.TIME DESC) AS TIME,
FIRST_VALUE(IO) OVER (PARTITION BY lms_attendance.USER ORDER BY lms_attendance.TIME DESC) AS IO
FROM lms_attendance;
Result:
| ID | USER | TIME | IO |
--------------------------------
| 2 | 9 | 1370931664 | out |
| 3 | 6 | 1370932128 | out |
| 5 | 12 | 1370933037 | in |
The advantage I see over using the solution proposed by Justin is that it enables you to select the row with the most recent data per user (or per id, or per whatever) even from subqueries without the need for an intermediate view or table.
And in case your running a HANA it is also ~7 times faster :D
Ok, this might be either a hack or error-prone, but somehow this is working as well-
SELECT id, MAX(user) as user, MAX(time) as time, MAX(io) as io FROM lms_attendance GROUP BY id;
select b.* from
(select
`lms_attendance`.`user` AS `user`,
max(`lms_attendance`.`time`) AS `time`
from `lms_attendance`
group by
`lms_attendance`.`user`) a
join
(select *
from `lms_attendance` ) b
on a.user = b.user
and a.time = b.time
I have tried one solution which works for me
SELECT user, MAX(TIME) as time
FROM lms_attendance
GROUP by user
HAVING MAX(time)
I have a very large table and all of the other suggestions here were taking a very long time to execute. I came up with this hacky method that was much faster. The downside is, if the max(date) row has a duplicate date for that user, it will return both of them.
SELECT * FROM mb_web.devices_log WHERE CONCAT(dtime, '-', user_id) in (
SELECT concat(max(dtime), '-', user_id) FROM mb_web.devices_log GROUP BY user_id
)
select result from (
select vorsteuerid as result, count(*) as anzahl from kreditorenrechnung where kundeid = 7148
group by vorsteuerid
) a order by anzahl desc limit 0,1
I have done same thing like below
SELECT t1.*
FROM lms_attendance t1
WHERE t1.id in (SELECT max(t2.id) as id
FROM lms_attendance t2
group BY t2.user)
This will also reduce memory utilization.
Thanks.
Possibly you can do group by user and then order by time desc. Something like as below
SELECT * FROM lms_attendance group by user order by time desc;
Try this query:
select id,user, max(time), io
FROM lms_attendance group by user;
This worked for me:
SELECT user, time FROM
(
SELECT user, time FROM lms_attendance --where clause
) AS T
WHERE (SELECT COUNT(0) FROM table WHERE user = T.user AND time > T.time) = 0
ORDER BY user ASC, time DESC
I have the table:
id | date_submitted
1 | 01/01/2017
1 | 01/02/2017
2 | 01/03/2017
2 | 01/04/2017
I'm looking for the correct SQL to select each row, limited to one row per id that has the latest value in date_submitted.
So the SQL should return for the above table:
id | date_submitted
1 | 01/02/2017
2 | 01/04/2017
The query needs to select everything in the row, too.
Thanks for your help.
You can find max date for each id in subquery and join it with the original table to get all the rows with all the columns (assuming there are more columns apart from id and date_submitted) like this:
select t.*
from your_table t
inner join (
select id, max(date_submitted) date_submitted
from your_table
group by id
) t2 on t.id = t2.id
and t.date_submitted = t2.date_submitted;
Note that this query will return multiple rows for an id in case there are multiple rows with date_submitted equals to max date_submitted for that id. If you really want only one row per id, then the solution will be a bit different.
If you just need id and max date use:
select id, max(date_submitted) date_submitted
from your_table
group by id
I would like to fetch one row in my MySQL database for every value in an array. What I'm trying to do is get the posts which were most recently voted on. The votes table has the following structure
| id | postid | voter | vote type | time |
|====|========|=======|===========|============|
| 1 | 1 | 1 | 1 | 1445389824 |
| 2 | 2 | 6 | 1 | 1445408529 |
| 3 | 1 | 5 | 2 | 1445435978 |
I would like to select the posts that were most recently voted on, in the order they were voted on. So, for example, because the ids of the votes ordered by time from greatest to lowest is 3, 2, 1, I would like to select the post ids 1, 2, 1. But, because 1 appears twice, I would only like to select the first one, so the final result would be 1, 2.
This table is going to be very, very large, so selecting every post id and then trimming it to the desirable array using php doesn't seem like a very good idea.
Also, only the posts that are in an array should be selected. For example, selecting all of the posts without omitting duplicates would be
SELECT `postid`
FROM `votes`
WHERE `postid` IN ($posts)
ORDER BY `time` DESC
But by using this method, I would have to get rid of the duplicate entries using php, which seems like it would be very intensive.
I would also like to select the number of votes on each post in the list. I could do this in a separate query, but doing it in one would probably be faster. So, for example
SELECT COUNT(`id`)
FROM `votes`
WHERE `postid` IN ($posts)
ORDER BY `time` DESC
Would select all of the votes on the posts given. Instead, I would like it to select an array of the votes for each post, or something that could be converted to that.
Is there any MySQL operator that would allow me to select the number of votes on each post included in the array, and order them by the time the most recent post was voted on? In the above table, because there are 2 votes on post 1, and 1 vote on post 2, the result would be
array("1" => 2, "2" => 1)
Here is a possible query to get both the time of the latest vote and vote count per post:
SELECT `postid`,
MAX(time) as time,
COUNT(*) as vote_count
FROM `votes`
WHERE `postid` IN ($posts)
GROUP BY `postid`
ORDER BY 2 DESC
If you want all the other fields of these latest votes records, then you could use the above as a sub-query of a larger one:
SELECT `id`, `postid`, `voter`,
`vote_type`, `time`, vote_count
FROM `votes` v
INNER JOIN (
SELECT `postid`,
MAX(time) as time,
COUNT(*) as vote_count
FROM `votes`
WHERE `postid` IN ($posts)
GROUP BY `postid`) filter
ON v.`postid` = filter.`postid`
AND v.`time` = filter.time
ORDER BY `time` DESC
So you want to get the latest vote for each post in an array. I think you can just add a GROUP BY clause.
SELECT `postid`, COUNT(postid) AS votecount
FROM `votes`
WHERE `postid` IN ($posts)
GROUP BY `postid`
ORDER BY MAX(`time`)
This one's been tricky to quantify, so I may not have this question worded properly first time around.
I have a table following a format similar to this:
| id | other_id | timestamp |
| 1 | 1 | 2012-01-01 |
| 2 | 1 | 2012-01-02 |
| 3 | 2 | 2012-01-02 |
What I am attempting to do is, given the record with 'id' 2, and similar records, for which the 'id' column value is known and is unique and the 'other_id' is known corresponding with it, how do I find, for each, the 'id' of the record having the same 'other_id' but the first lower 'id' than the one I already know.
E.g.
$arrKnownIds = array (
0 => array('id'=>2,'other_id'=>1),
1 => array('id'=>3,'other_id'=>2)
);
With this info, I'd like to run a query such that this results:
while($row = mysql_fetch_assoc($result)) {
$arrPreviousIds[$row['other_id']] = $row['id'];
// having in this case values of:
// $row['other_id'] = 2;
// $row['id'] = 1;
}
I can't quite work out if I need to tackle this using UNION, multiple php query statements or if there's another way.
Any thoughts on how to tackle this one are greatly appreciated.
Thanks :)
Edit - The original query takes the following form:
SELECT DISTINCT(`other_id`), MAX(`id`), MAX(`timestamp`)
FROM `event`
GROUP BY `other_id`
ORDER BY `id` DESC, `other_id` ASC
LIMIT 0, 10
// This is intended to get the last 10 unique events and find when they occurred.
// From this, I then try to find when they previously occurred.
How about this?
SELECT t1.id, (SELECT id
FROM tbl t2
WHERE t2.other_id = t1.other_id
AND t2.id < t1.id
ORDER BY t2.id DESC
LIMIT 1)
FROM tbl t1
WHERE t1.id IN (1,2,3)
There are more efficient ways of doing this if you will be dealing with large result sets. Can you explain exactly how you will be using this query?
UPDATE - based on addition of existing query to question here is an updated query to combine the two -
SELECT tmp.*, (SELECT `timestamp`
FROM `event`
WHERE `event`.`other_id` = `tmp`.`other_id`
AND `event`.`id` < `tmp`.`id`
ORDER BY `event`.`id` DESC
LIMIT 1) AS `prev_timestamp`
FROM (
SELECT `other_id`, MAX(`id`) AS `id`, MAX(`timestamp`) AS `timestamp`
FROM `event`
GROUP BY `other_id`
ORDER BY `id` DESC, `other_id` ASC
LIMIT 0, 10
) tmp
I have not tried this but it should give the desired result.