i have a comments table, like this:
id, answer_id, content
now i want to get latest 10 comments for EACH answer id.
list of answer ids are provided like (1,5,11,27,82)
is it possible to get all related comments by just one query ?
i currently do this by php's foreach:
foreach ($answers as $answer) { // query mysql for its comments
You can use UNION ALL for each answer_id:
(select id, answer_id, content from comments where answer_id=1 order by id desc limit 10)
union all
(select id, answer_id, content from comments where answer_id=5 order by id desc limit 10)
union all
(select id, answer_id, content from comments where answer_id=11 order by id desc limit 10)
union all
(select id, answer_id, content from comments where answer_id=27 order by id desc limit 10)
union all
(select id, answer_id, content from comments where answer_id=82 order by id desc limit 10);
This is a pain in MySQL, but you can use variables:
select c.*
from (select c.*,
(#rn := if(#a = c.answer_id, #rn + 1,
if(#a := c.answer_id, 1, 1)
)
) as rn
from comments c cross join
(select #rn := 0, #a := -1) params
order by answer_id, id desc
) c
where rn <= 10;
This assumes that larger values of id are more recent.
Related
This question already has answers here:
Rank function in MySQL
(13 answers)
Closed 4 years ago.
SELECT u.user_id, u.user_uid, s.ostats, s.attack, s.defense
FROM stats s JOIN
users u
ON s.id = u.user_id
ORDER BY s.ostats DESC;
So in above data, "ostats"(overall) is just a sum of attack+defense and by using this query I could display users in descending order of their "ostats" values..
But how do I assign and display rank of each user, like the one with most "ostats" valued user as Rank 1 and the second highest "ostats" valued user as Rank 2 and so on..?
What about using a variable to keep track of the row number?
SET #rank = 0;
SELECT
u.user_id,
u.user_uid,
s.ostats,
s.attack,
s.defense,
(#rank:=#rank + 1) AS rank
FROM stats s
JOIN users u on s.id = u.user_id
ORDER BY s.ostats DESC;
You can assign a row number using variables:
SELECT u.user_id,u.user_uid, s.ostats, s.attack, s.defense,
s.ranking
FROM (SELECT s.*, (#rn := #rn + 1) as ranking
FROM (SELECT s.* FROM stats s ORDER BY s.ostats DESC) s CROSS JOIN
(SELECT #rn := 0) params
) s JOIN
users u
ON s.id = u.user_id
ORDER BY s.ostats DESC;
In the event of ties, this will give different users different rankings. If that is an issue, you can use this modified form:
SELECT u.user_id,u.user_uid, s.ostats, s.attack, s.defense,
s.ranking
FROM (SELECT s.*,
(#rn := if(#o = ostats, #rn,
if(#o := ostats, #rn + 1, #rn + 1)
)
) as ranking
FROM (SELECT s.* FROM stats s ORDER BY s.ostats DESC) s CROSS JOIN
(SELECT #rn := 0, #o := -1) params
) s JOIN
users u
ON s.id = u.user_id
ORDER BY s.ostats DESC;
Of course, in MySQL 8.0, you can use row_number(), rank() or dense_rank() for this purpose.
I am struggling to find an optimal solution for the following problem.
Suppose I have a table 'Table' like this:
id name report_id
1 name1 1
2 name2 3
3 name3 5
4 name1 7
5 name3 8
....................
I want to select for each value in a set: ('name1', 'name2') 10 random unique rows.
Of course it is possible to do with union like:
(SELECT * FROM Table
WHERE
name='name1'
ORDER BY RAND() LIMIT 10)
UNION
(SELECT * FROM Table
WHERE
name='name2'
ORDER BY RAND() LIMIT 10)
But if I have 100 unique names for which I have to select 10 random records - this query is going to be a bit large.
SQLFiddle demo
select ID,NAME,REPORT_ID
from
(
select *, #row:=if(name=#name,#row,0)+1 as rn, #name:=name from
(select *,RAND() as trand from t) t1,
(select #row:=0,#name:='') tm2
order by name,trand
) t2
where rn<=10
Try this:
SELECT
id,
name,
report_id
FROM
(
SELECT id,
report_id,
name,
CASE WHEN #name != name THEN #rn := 1 ELSE #rn := #rn + 1 END rn,
#name:=name
FROM (SELECT * FROM tbl ORDER BY RAND()) a,
(SELECT #rn:=0, #name := NULL) r
ORDER BY name
) s
WHERE rn <= 10;
SQL FIDDLE DEMO
This doesn't work in MySQL, but in PostgreSQL you can use partition by
select name,report_id from
(select name,report_id,row_number()
over
(partition by name order by random())
as rn from Table) a
where rn<=10
I had this same question and found this answer from a colleague.
I have a query that gets me a users rank in a table of scores.
SELECT
*
FROM
(SELECT
*, #rank:=#rank + 1 rank
FROM
(SELECT
user_id, SUM(round_total) TotalPoints
FROM
sx14sp_mem_picks
GROUP BY user_id) s, (SELECT #rank:=0) init
ORDER BY TotalPoints DESC) r
WHERE
user_id = 22234
There is a problem with ties. I have a table field "pick_date" that i would like to use to break ties with. The user who made his picks first beats the tie.
Any ideas?
If sx14sp_mem_picks.pickdate is the field to break ties then in the order by sx14sp_mem_picks subquery, add
min( pickdate) asc
This will put the earliest pickdate first - you have to use MIN() bc you need to use an aggregate function given the use of "group by".
You need to order by the pick date in addition to the total points. However, you are talking about multiple rows per user. So, let's take the last pick date:
SELECT *
FROM (SELECT *, (#rank:=#rank + 1) as rank
FROM (SELECT user_id, SUM(round_total) as TotalPoints, max(pick_date) as max_pick_date
FROM sx14sp_mem_picks
GROUP BY user_id
) s CROSS JOIN
(SELECT #rank := 0) init
ORDER BY TotalPoints DESC, max_pick_date asc
) r
WHERE user_id = 22234;
I found some good answers for this question, but I can't really get them to work.
I wan't to get a players rank from a hiscore table.
id name score
1 John 10
2 Linda 5
3 Emmy 25
I want to pass in a name in the query (Linda) and get her rank (She only have 5 points in the table above), and get her rank (nr 3).
I found a similar question with this answer, but don't understand it:
SELECT uo.*,
(
SELECT COUNT(*)
FROM users ui
WHERE (ui.points, ui.id) >= (uo.points, uo.id)
) AS rank
FROM users uo
WHERE id = #id
Thanks in advance
SELECT (COUNT(*) + 1) AS rank FROM hiscore WHERE score > (SELECT score FROM hiscore WHERE name = 'Linda')
Try this query -
SELECT name, score, rank FROM
(SELECT *, #r:=#r + 1 rank FROM table_name ORDER BY score DESC) t1,
(SELECT #r:=0) t2
WHERE name = 'Linda'
SET #rownum := 0;
SELECT rank, name, score
FROM
(SELECT #rownum := #rownum + 1 AS rank, name, score
FROM players
ORDER BY score DESC)
Here is my query:
SELECT * FROM Photos WHERE Event_ID IN ($eventidstring)
I know I can limit the total amount of results from this query using LIMIT 5
I need the Limit the amount of results Per value in $eventidstring.
So if $eventidstring = 23,41,23*
*And there are 10 results WHERE Event_ID = 23, I want to limit this amount to 5. The same for all the other values in $eventidstring.
You may have some joy doing something similar to Oracle's RANK by PARITION in MySQL.
Sadly this feature is not available in MySQL though you can work around it using this method
Dump that in an inline view and then select those rows with rank <= 5;
Hence:
SELECT t.* FROM (
SELECT (
CASE Event_id
WHEN #curEventId
THEN #curRow := #curRow + 1
ELSE #curRow := 1 AND #curEventId := Event_Id END
) AS rank,
p.*
FROM Photos p INNER JOIN (SELECT #curRow := 0, #curEventId := '') r
ORDER BY p.Event_Id DESC
) t
WHERE t.rank <= 5 ORDER BY t.Event_Id asc;
Consider how you are going to 'choose' the top five by Event_Id too. You can always add in more after the ORDER BY p.Event_Id DESC to decide this.
I take it you're writing that query somewhere inside your PHP, so you need to split the $eventidstring into it's component values, form a SELECT for each and UNION all after the first one.
You sould do this with a loop of some sort, and concatenate the query strings in the loop...
If I understand correctly and you want to get five of each, you can use this:
(SELECT * FROM Photos WHERE Event_ID = 23 LIMIT 5)
UNION
(SELECT * FROM Photos WHERE Event_ID = 41 LIMIT 5)
UNION
(SELECT * FROM Photos WHERE Event_ID = ... LIMIT 5)
...
Maybe with a SELECT UNION but you need a new select for each value:
SELECT * FROM Photos WHERE Event_ID = 23 LIMIT 5
UNION SELECT * FROM Photos WHERE Event_ID = 41 LIMIT 5
UNION SELECT ...