How to execute Multiplication Operation in a Mysql Query?

If my query is like this :

"SELECT registration.hosteladmissionno,
   registration.student_name,
   registration.semester,
   student_month.hosteladmissionno,
   student_month.student_name,
   student_month.semester,
   messexp.billmonth,messexp.billyear ,messexp.perdayrate,student_month.days_mess
   FROM registration,
    student_month ,messexp,blockexp
   WHERE  student_month.hosteladmissionno = registration.hosteladmissionno
    ";

How to execute multiplication operation within this query? say.. multiplication operation btw days_mess and

The multiplication operator is * :

mysql> select 100 * 2;
+---------+
| 100 * 2 |
+---------+
|     200 |
+---------+
1 row in set (0.00 sec)

In your case, if you want to multiply the values of two columns, you can use those columns, with the * operator between them :

select column1 * column2 as result
from your_table
where ...

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