MySQL user defined functions

问题:

I have a table contains a few columns say: column_1, column_2 and column_3.

I appended an new column to the table called score. What I want to do is calculate the score based on these three columns and tune the parameters easily.

Say my score formula looks like below:

score = a * column_1 + b * column_2 + c * column_3

is it possible to create a udf or process(never used before) to easily do that?

so I have a function like getScore(a,b,c) and I could do something like:

select 
    column_1,
    column_2, 
    column_3, 
    getScore(0.5, 0.1, 0.4) as score
from table

or

update table set score = getScore(0.5, 0.1, 0.4)

Thanks!

回答1:

Yes.

CREATE FUNCTION `getScore`(`a` DECIMAL(12,4), `b` DECIMAL(12,4), `c` DECIMAL(12,4)) RETURNS DECIMAL(12,4)
BEGIN
    RETURN a + b + c;
END

SELECT getScore(0.3, 0.4, 0.5)
-> 1.2000

But if you need some values from the table, you need to include those as parameters too.

SELECT getScore(column1, column2, column3, 0.5, 0.1, 0.4) AS score FROM table