Points on highest record in Mysql - mysql

Question

My table
+------+-------+--------+
| NAME | MARKS | POINTS |
+------+-------+--------+
| S1 | 53 | (null) |
| S2 | 55 | (null) |
| S3 | 56 | (null) |
| S4 | 55 | (null) |
| S5 | 52 | (null) |
| S6 | 51 | (null) |
| S7 | 53 | (null) |
+------+-------+--------+
Refer : http://www.sqlfiddle.com/#!2/5d046/1
I would like to add 3,2,1 points to the highest Marks. Here S3 goes to 3 points, S2,S4 goes to 2 points and S1,S7 goes to 1 points.
Final outputs looks,
+------+-------+--------+
| NAME | MARKS | POINTS |
+------+-------+--------+
| S1 | 53 | 1 |
| S2 | 55 | 2 |
| S3 | 56 | 3 |
| S4 | 55 | 2 |
| S5 | 52 | 0 |
| S6 | 51 | 0 |
| S7 | 53 | 1 |
+------+-------+--------+
Plz help

Answer 1

My suggestion is that you first calculate the ranking of each mark, and then use that in a case statement in an update.
The following query shows one way to calculate the ranking:
select t.*,
#rn := if(#marks = marks, #rn, #rn + 1) as ranking,
#marks := marks
from myTable t cross join
(select #rn := 0, #marks := -1) const
order by t.marks desc;
(As a note: I am a bit uncomfortable with this method, because MySQL does not guarantee the order of evaluation of the two expressions with constants. If #marks were set before #rn, then it wouldn't work. In practice, that does not seem to happen. And, this is more efficient that the equivalent with a correlated subquery.)
You can then put this into an update using join:
update myTable join
(select t.*,
#rn := if(#marks = marks, #rn, #rn + 1) as ranking,
#marks := marks
from myTable t cross join
(select #rn := 0, #marks := -1) const
order by t.marks desc
) mr
on myTable.Name = mr.Name
set myTable.Points := (case when mr.ranking = 1 then 3
when mr.ranking = 2 then 2
when mr.ranking = 3 then 1
else 0
end);
This has been tested on your SQL Fiddle.

Answer 2

You can do it via variables (see samples in other answers), or via case:
select
myTable.*,
case
when max1.marks is not null then 3
when max2.marks is not null then 2
when max3.marks is not null then 1
else 0
end as score
from
myTable
LEFT JOIN
(select marks from myTable order by marks desc limit 1) AS max1
ON myTable.marks=max1.marks
LEFT JOIN
(select marks from myTable order by marks desc limit 2,1) AS max2
ON myTable.marks=max2.marks
LEFT JOIN
(select marks from myTable order by marks desc limit 3,1) AS max3
ON myTable.marks=max3.marks;
the demo can be found here.

Answer 3

UPDATE myTable t1
INNER JOIN
(
SELECT #row:=#row-1 AS RowPoints, Marks
FROM (
SELECT Marks
FROM myTable
GROUP BY Marks
ORDER BY Marks DESC
LIMIT 3
) AS TopMarks
INNER JOIN (SELECT #row:=4) AS RowInit
) AS AddPoints ON t1.Marks = AddPoints.Marks
SET Points = COALESCE(Points, 0) + AddPoints.RowPoints;
This should work just fine. You should and and index on the Marks column.

Answer 4

The simplest way to do this:
SELECT t.Name Name, t.Marks Marks,
(CASE WHEN Marks = (Select max(marks) from mytable) THEN 3 ELSE 0 END+
CASE WHEN Marks = (Select min(marks) from (Select distinct marks
from mytable order by marks desc limit 2) a) THEN 2 ELSE 0 END+
CASE WHEN Marks = (Select min(marks) from (Select distinct marks
from mytable order by marks desc limit 3) b) THEN 1 ELSE 0 END)
AS `Points`
FROM mytable t;
SQL Fiddle