MySQL - 根据该列乘以值

Question

我该怎么写这个..我有一个表“公司”，其中有一列“大小”。大小引用枚举。当“大小”列为时，我需要通过替换“大小”列来将平均公司规模显示为别名 AS“AverageEstimatedCompanySize”:

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

换句话说，我的表格将公司规模显示为 1、2、3、4 或 5。而 1 实际上是公司规模 15。

这都是更大查询的一部分:

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

听起来像是可以用 case statement 解决的问题。以下内容未经测试，但应该为您指明正确的方向。

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')))