PHP算法和MySQL [关闭]

Question

I have an equation that I need to process from a couple MySQL columns. I am just trying to figure out the best way of doing this once I run my SELECT statement to retrieve all the data.

Table - tbl_Spirits
Columns - ID, Volume, Proof

I know how to retrieve all the Data from MySQL, the problem is, is that there may be one record returned or 5. Probably never more then 5. Is there a clean fast method of the equation below in PHP.

This example is if there was 2 records returned.

((Volume1 * Proof1) + (Volume2 * Proof2)) / (Volume1 + Volume2) 

Answer 1

Even if you did not show any attempt to solve your problem, I will give it a try. Basically you want to divide the sum of products between the two columns by the sum from one of them. So it should be something like

SELECT 
    SUM(`Volume`*`Proof`)/SUM(`Volume`) 
FROM 
    `tbl_Spirits` 
WHERE 
    1 

and you will need to fill in your WHERE statement to fit your needs

Update: added this sample in sqlfiddle: http://sqlfiddle.com/#!2/0dc417/1/0 you will see that for the two records the value you will get is 4, exactly (2*4+3*4)/(2+3)