How to find neighbour order by another colum mysql - php

Question

My problem is,
I have a table in mysql
which colums are
id Student score
1 A 55
2 B 86
3 C 65
4 D 23
5 E 84
6 F 45
7 G 80
I want to find rank of any student in whole class based on score, with the student who scored just greater them him and an another student who scored just less them him.
for example if I am searching for student E
then output should be
id User score rank_in_classs
2 B 86 1
5 E 84 2
7 G 80 3
An another example can be that if I am looking for student A
id User score rank_in_classs
3 c 65 4
1 A 55 5
6 F 45 6
How can I find it using mysql query.
Thanks

Answer 1

Query
SELECT id, Student, score,
FIND_IN_SET( score, (
SELECT GROUP_CONCAT( score
ORDER BY score DESC )
FROM tbl )
) AS rank_in_class
FROM tbl
ORDER BY rank_in_class
LIMIT 3;
DEMO

Answer 2

Using the FIND_IN_SET() based solution proposed by Ullas you can locate a particular student +/- 1 rank this way:
set #this_rank := (
SELECT
FIND_IN_SET( score, (
SELECT GROUP_CONCAT( score
ORDER BY score DESC )
FROM tbl
)
) AS rank_in_class
FROM tbl
where student = 'A'
);
select
*
from (
SELECT
id
, Student
, score
, FIND_IN_SET( score, (
SELECT GROUP_CONCAT( score
ORDER BY score DESC )
FROM tbl
)
) AS rank_in_class
FROM tbl
) ric
where rank_in_class between #this_rank-1 AND #this_rank+1
ORDER BY rank_in_class
LIMIT 3;
Note: IF you stored the rank value in the table, then this would not be so cumbersome and could perform way better.

Answer 3

The best way to do that is probably with a mix of two queries and a little of PHP.
The first query retrieves the rank of the "focused" student you want;
The second query retrieves the range of all the students around the focused "student" with a dynamic LIMIT statement (this is where the use of PHP is unavoidable);
So something like this would probably do the job :
$user = 'C'; // Student user we want to "focus"
$range = 1; // Range around the "focus" : 1 before and 1 after (could be changed to anything else)
// First query : retrieving the rank of the "focused" student
$stmt = $mysqli->prepare('SELECT COUNT(*) AS Rank FROM Student AS Focused INNER JOIN Student as Others ON Others.Score > Focused.Score OR (Others.Score = Focused.Score AND Others.Id > Focused.Id) WHERE Focused.user = ?');
$stmt->bind_param('s',$user);
$stmt->execute();
$res = $stmt->get_result()->fetch_assoc();
$startRank = $res['Rank'];
// Computing the dynamic LIMIT
if (($startRank - $range) < 1) {
$offset = 0;
$rowCount = $startRank + $range + 1;
} else {
$offset = $startRank - $range;
$rowCount = ($range * 2)+1;
}
// Second query : retrieving the rank of all the students around the "focused" student
$stmt = $mysqli->prepare('SELECT id, user, score, #curRank := #curRank + 1 AS rank FROM Student, (SELECT #curRank := ?) Rank ORDER BY Score DESC, id DESC LIMIT ?, ?');
$stmt->bind_param('iii',$offset,$offset,$rowCount);
$stmt->execute();
This is probably the most optimized way to query the database to get what you want. As a bonus, you can change the range to whatever you like.