get rank in marks database in mysql
Just add the word DISTINCT in front of the first marks inside the GROUP_CONCAT function

SELECT id, marks, FIND_IN_SET( marks, (
SELECT GROUP_CONCAT( DISTINCT marks
ORDER BY marks DESC ) 
FROM exam )
) AS rank
FROM exam;


First here is the sample data

use test
DROP TABLE IF EXISTS exam;
CREATE TABLE exam
(
    id int not null auto_increment,
    marks int not null,
    primary key (id)
);
INSERT INTO exam (marks)
VALUES (7),(10),(7),(10),(9);
SELECT * FROM exam;


Let's load the sample data

mysql&gt; use test
Database changed
mysql&gt; DROP TABLE IF EXISTS exam;
Query OK, 0 rows affected, 1 warning (0.04 sec)

mysql&gt; CREATE TABLE exam
    -&gt; (
    -&gt;     id int not null auto_increment,
    -&gt;     marks int not null,
    -&gt;     primary key (id)
    -&gt; );
Query OK, 0 rows affected (0.06 sec)

mysql&gt; INSERT INTO exam (marks)
    -&gt; VALUES (7),(10),(7),(10),(9);
Query OK, 5 rows affected (0.06 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql&gt; SELECT * FROM exam;
+----+-------+
| id | marks |
+----+-------+
|  1 |     7 |
|  2 |    10 |
|  3 |     7 |
|  4 |    10 |
|  5 |     9 |
+----+-------+
5 rows in set (0.02 sec)


Now, watch the output of the proposed query:

mysql&gt; SELECT id, marks, FIND_IN_SET( marks, (
    -&gt; SELECT GROUP_CONCAT( DISTINCT marks
    -&gt; ORDER BY marks DESC )
    -&gt; FROM exam )
    -&gt; ) AS rank
    -&gt; FROM exam;
+----+-------+------+
| id | marks | rank |
+----+-------+------+
|  1 |     7 |    3 |
|  2 |    10 |    1 |
|  3 |     7 |    3 |
|  4 |    10 |    1 |
|  5 |     9 |    2 |
+----+-------+------+
5 rows in set (0.00 sec)

mysql&gt;


Give it a Try !!!