你能在别名的时候用大小写分组吗？

Question

我有一个SELECT语句正在从CASE WHEN THEN状态（或者可以使用多个IF语句）中计算，别名为“长度”，我需要正确地将结果组合在一起。SELECT似乎在工作，但是组将它们分组错误。以下是我的声明：

SELECT CASE 
    WHEN DATEDIFF(o.EndDate, o.StartDate) < 30 THEN '<1 Month'
    WHEN DATEDIFF(o.EndDate, o.StartDate) < 90 THEN '1 - 2 Months'
    WHEN DATEDIFF(o.EndDate, o.StartDate) < 210 THEN '3 - 4 Months'
    ELSE '>4 Months' END AS 'Length', 
    COUNT(DISTINCT(person.ID)) AS 'COUNT'
FROM person
    INNER JOIN opportunity AS o
    INNER JOIN Organization AS org
    ON person.EntityID = o.id 
        AND O.OrganizationID = Org.ID
WHERE person.TitleID = 2
    AND o.bID = 1
GROUP BY 'Length'
ORDER BY 'Length' ASC;

这将所有结果分为“3-4个月”，这是不对的。。

Answer 1

您可以通过如下方式引用select中的语句对其进行分组。另见这个问题。

SELECT CASE 
    WHEN DATEDIFF(o.EndDate, o.StartDate) < 30 THEN '<1 Month'
    WHEN DATEDIFF(o.EndDate, o.StartDate) < 90 THEN '1 - 2 Months'
    WHEN DATEDIFF(o.EndDate, o.StartDate) < 210 THEN '3 - 4 Months'
    ELSE '>4 Months' END AS 'Length', 
    COUNT(DISTINCT(person.ID)) AS 'COUNT'
FROM person
    INNER JOIN opportunity AS o
    INNER JOIN Organization AS org
    ON person.EntityID = o.id 
        AND O.OrganizationID = Org.ID
WHERE person.TitleID = 2
AND o.bID = 1
GROUP BY 1
ORDER BY 1 ASC;

Answer 2

我一直在努力解决同样的问题，下面是我提出的解决方案：

SELECT CASE 
WHEN DATEDIFF(o.EndDate, o.StartDate) < 30 THEN '<1 Month'
WHEN DATEDIFF(o.EndDate, o.StartDate) < 90 THEN '1 - 2 Months'
WHEN DATEDIFF(o.EndDate, o.StartDate) < 210 THEN '3 - 4 Months'
ELSE '>4 Months' END AS `Length`, 
COUNT(DISTINCT(person.ID)) AS `COUNT`
FROM person
INNER JOIN opportunity AS o
INNER JOIN Organization AS org
ON person.EntityID = o.id 
    AND O.OrganizationID = Org.ID
WHERE person.TitleID = 2
AND o.bID = 1
GROUP BY `Length`
ORDER BY `Length` ASC;

Answer 3

如果没有将CASE语句包装到子查询中，则需要在GROUPBY子句中使用整个CASE语句。

SELECT  CASE 
            WHEN DATEDIFF(o.EndDate, o.StartDate) < 30 THEN '<1 Month'
            WHEN DATEDIFF(o.EndDate, o.StartDate) < 90 THEN '1 - 2 Months'
            WHEN DATEDIFF(o.EndDate, o.StartDate) < 210 THEN '3 - 4 Months'
            ELSE '>4 Months' 
        END AS `Length`, 
        COUNT(DISTINCT(person.ID)) AS `COUNT`
FROM    person
        INNER JOIN opportunity AS o
            ON person.EntityID = o.id
        INNER JOIN Organization AS org
            ON o.OrganizationID = Org.ID
WHERE   person.TitleID = 2
        AND o.bID = 1
GROUP   BY  CASE 
                WHEN DATEDIFF(o.EndDate, o.StartDate) < 30 THEN '<1 Month'
                WHEN DATEDIFF(o.EndDate, o.StartDate) < 90 THEN '1 - 2 Months'
                WHEN DATEDIFF(o.EndDate, o.StartDate) < 210 THEN '3 - 4 Months'
                ELSE '>4 Months' 
            END
ORDER   BY Length ASC;

还删除ORDER BY子句中列名周围的单引号。