如何在mysql中插入一些公式？

我想计算“柜台”桌上的一行。我试着把我的桌子做成：

name          black     yellow     white        qty_job      total
david           1        0          0            2             ?
andrew          0        1          1            4              ?

计算公式为：

total = (nblack * 1) + (nyellow * 1) + (nwhite * 0.4) / qty_job
total = (1 * 1) + (0 * 1) + (0 * 0.4) / 2 = 0.5

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如何在mysql代码中插入此公式？尤其是在SELECT方法中。

您不应该/不能使用某个公式排一行。您应该使用此查询检索总计：

SELECT
    name,
    black,
    yellow,
    white,
    qty_job
    (SUM(black) + SUM(yellow) + SUM(white)*0.4) / qty_job AS total
FROM counter
GROUP BY name;

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另一种方法是创建视图：

CREATE VIEW test AS
SELECT id, (black * 1) + (yellow * 1) + (white * 0.4) / qty_job as total FROM counter;

剩下的应该很简单，你可以这样做：

select
 counter.id,
 black,
 yellow,
 white,
 test.total
from
 counter,
 test
where
  counter.id = test.id

DECLARE @Number As int, @Number2 As int
SET @Number = 5
WHILE @Number >= 1
BEGIN
PRINT @Number
SET @Number = @Number - 1

PRINT @Number2
SET @Number2 = @Number * (@Number2 - 1)

PRINT 'The Factorial of'
PRINT @Number
PRINT 'is'
PRINT @Number2

END 
GO