MySQL - 根据该列乘以列的值

Question

我怎么写这个..我的表'公司'有一个'大小'列。大小引用枚举。当“尺寸”列为：

时，我需要通过替换列'尺寸'来将平均公司尺寸显示为别名AS'AverageEstimatedCompanySize'

1 = 15
2 = 30
3 = 50
4 = 100
5 = 250

换句话说，我的表格显示公司规模为1,2,3,4或5.而1实际上是公司规模为15.

这是更大查询的所有部分：

SELECT COUNT(DISTINCT(ID)) AS 'Total # of Opps', AVG(Size*?) AS 'AverageEstimatedCompanySize'
FROM persontable AS POJT INNER JOIN opportunity
ON POJT.ID = opportunity.id
WHERE opportunity.TimeStamp >= '2012-01-01' AND opportunity.TimeStamp <= '2012-12-31' AND POJT.JobTitleID IN 
    (SELECT Id
    FROM job
    WHERE CategoryID IN 
        (SELECT id
        FROM job_category
        WHERE name IN ('Sc', 'Ma', 'Co', 'En', 'Tr')))

Answer 1

听起来像case statement可以解决的问题。以下是未经测试但应指向正确的方向。

SELECT 
    COUNT(DISTINCT(ID)) AS 'Total # of Opps', 
    AVG(
        CASE Size
            WHEN 1 THEN 15
            WHEN 2 THEN 30
            WHEN 3 THEN 50
            WHEN 4 THEN 100
            WHEN 5 THEN 250
        END
    ) AS 'AverageEstimatedCompanySize'
FROM persontable AS POJT INNER JOIN opportunity
ON POJT.ID = opportunity.id
WHERE opportunity.TimeStamp >= '2012-01-01' AND opportunity.TimeStamp <= '2012-12-31' AND POJT.JobTitleID IN 
    (SELECT Id
    FROM job
    WHERE CategoryID IN 
        (SELECT id
        FROM job_category
        WHERE name IN ('Sc', 'Ma', 'Co', 'En', 'Tr')))

Answer 2

我认为一种方法可能是将查询适当地修改为JOIN到Company表（这是你需要解决的问题），然后修改{{1声明：

AVG

其中... AVG(CASE `Size` WHEN 1 THEN 15 WHEN 2 THEN 30 WHEN 3 THEN 50 WHEN 4 THEN 100 WHEN 5 THEN 250 END) AS 'AverageEstimatedCompanySize' 来自Size表。

现在，一种更加动态的方法是创建一个新字段，甚至是一个新表，它映射这些大小并只Company JOIN表，并在查询中说出新表然后每行抓取相应的字段。这将摆脱Company声明。