Mysql乘法运算

Question

如何在Mysql查询中执行乘法运算？

如果我的查询是这样的：

"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
    ";

如何在此查询中执行乘法运算？说..乘法运算btw days_mess和

Answer 1

乘法运算符为*：

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

在您的情况下，如果您想要将两列的值相乘，则可以使用这些列，并在它们之间使用*运算符：

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

Answer 2

select (days_mess * anotherFiled) as anyName

Answer 3

在文档中是否有一些令人困惑的东西： MySQL Reference: Arithmetic Functions？

SELECT registration.hosteladmissionno,
    ## ...
    messexp.billmonth,messexp.billyear ,messexp.perdayrate,student_month.days_mess
    ## additionally generated column:
    messexp.perdayrate * student_month.day_mess AS account_payable
    ## ... end additionally generated column

FROM registration，student_month，messexp，blockexp    student_month.hosteladmissionno = registration.hosteladmissionno

Answer 4

SELECT (student_month.days_mess *  anotehr_field ), 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
    ;