MySQL 您可以使用 CASE WHEN THEN 别名进行 GROUP BY 吗？
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Can you GROUP BY with a CASE WHEN THEN alias name?
提问by Ken
I have a SELECT statement being calculated from a CASE WHEN THEN state (or could use multiple IF statements) aliased as 'Length', and I need to correctly GROUP the results together. The SELECT seems to be working, but the group groups them wrong. Here is my statement:
我有一个 SELECT 语句是根据 CASE WHEN THEN 状态（或可以使用多个 IF 语句）计算的，别名为“长度”，我需要正确地将结果分组在一起。SELECT 似乎正在工作，但该组将它们分组错误。这是我的声明：
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;
This groups all results into '3 - 4 Months' which isn't right..
这将所有结果分组为“3 - 4 个月”，这是不对的。
回答by John Woo
You need to use the whole CASEstatement in the GROUP BYclause if you don't wrapped it in a subquery.
如果您不将其包装在子查询CASE中，GROUP BY则需要在子句中使用整个语句。
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;
Remove also the single quotes around the column name in the ORDER BYclause.
还删除ORDER BY子句中列名周围的单引号。
回答by Hannes
I was struggling with exactly the same problem and here is the solution I came up with:
我正在努力解决完全相同的问题，这是我想出的解决方案：
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;
