how to run sql query for sum of two or more rows in php file

The correct approach would be somewhat as follows:

DROP TABLE IF EXISTS my_table;

CREATE TABLE my_table
(id SERIAL PRIMARY KEY
,srno INT NOT NULL
,subject VARCHAR(20) NOT NULL
,mark INT NOT NULL
);

INSERT INTO my_table VALUES
(1,1,'english',52),
(2,1,'maths',52),
(3,1,'science',52);

SELECT srno
     , SUM(mark) total 
  FROM my_table
 GROUP 
    BY srno;
    +------+-------+
    | srno | total |
    +------+-------+
    |    1 |   156 |
    +------+-------+

Try something like this:

SELECT srno, name, english, maths, science, (english+maths+science) As TotalMarks FROM `table_name`

Check also this topic: How to SUM two fields within an SQL query

Well You can try these two methods:

select * from Your_Table_Name;

and when you display your result, you can add all these values like:

srno   name   english  maths  science  TotalMarks
$id    $name  $english $maths $science ($english+$maths+$science)

OR

select id, name, english, math, science, (english+maths+science) as Total from Your_Table_Name;

Try this :

SELECT *, (english + maths + science) AS Total FROM table;