sql - 按错误sql server分组

Question

select 
    case location_id 
      when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
      when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
      when 7 then 'MUMBAI' when 8 then 'CHENNAI' 
   end as CITY,
   count(*) as Total
from #tmptab1
group by CITY

我收到错误

消息 207，级别 16，状态 1，第 12 行
无效的列名称“城市”

如何纠正这个？请帮忙。

score 5 · Accepted Answer

您不能在GROUP BY子句中使用列别名。请参阅Select 语句的评估的概念顺序，您将在其中看到（逻辑上）按以下顺序评估子句：FROM, WHERE, GROUP BY, HAVING, SELECT, DISTINCT, UNION, ORDER BY。

这并不是引擎执行操作的确切方式，但它是一种有用的启发式方法，可以有效地理解为什么不能使用子句中SELECT语句中的某些GROUP BY内容——它在逻辑上不适用于GROUP BY子句后来评价。

有几种方法可以解决这个问题：

GROUP BY重复子句中的整个表达式：

SELECT
   City =
      CASE location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
      when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
      when 7 then 'MUMBAI' when 8 then 'CHENNAI'
      END,
   Total = Count(*)
FROM #tmptab1
GROUP BY
   CASE location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
   when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
   when 7 then 'MUMBAI' when 8 then 'CHENNAI'
   END

使用派生表：

SELECT
   City,
   Total = Count(*) 
FROM
   (
      SELECT
         City =
            CASE location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
            when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
            when 7 then 'MUMBAI' when 8 then 'CHENNAI'
            END
      FROM #tmptab1
   ) Cities
GROUP BY City;

使用公用表表达式 (CTE)、SQL Server 2005 及更高版本：

WITH Cities AS (
    SELECT
       City =
          CASE location_id 
             when 1 then 'DELHI' 
             when 2 then 'AHMEDABAD' 
             when 4 then 'HYDERABAD' 
             when 5 then 'KOLKATA' 
             when 6 then 'BANGALORE'
             when 7 then 'MUMBAI' 
             when 8 then 'CHENNAI'
          END
    FROM #tmptab1
)
SELECT
   City,
   Total = Count(*) 
FROM Cities
GROUP BY City;

使用 CROSS APPLY、SQL Server 2005 及更高版本：

SELECT
   City,
   Total = Count(*)
FROM
   #tmptab1
   CROSS APPLY (
      SELECT
         City =
            CASE location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
            when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
            when 7 then 'MUMBAI' when 8 then 'CHENNAI'
            END
   ) C
GROUP BY City;

由于您的表达式是确定性的，因此您可以简单地做GROUP BY location_id，但这不是正常情况，您不应该期望能够通过选择单个列来规避正常的聚合分组逻辑，因为大多数时间这样的 CASE 表达式增加了不确定的值。

事实上，因为信息不仅是确定性的，而且是关于现实世界的（而不是业务规则），我建议您不要在查询中编码这些信息！创建一个Location表并加入它。将可更改的用户数据直接放入查询中并不是最佳实践——查询应该记录过程，而不是内容，如果添加新的 location_id 会怎样？所有使用它的查询都必须改变。location_id此外，如果多个location_id可以引用同一个城市，分组依据将无法正常工作。

score 2 · Accepted Answer

您不能在 group by 语句中使用别名，您将需要 group by 中选择的整个部分

select case location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
when 7 then 'MUMBAI' when 8 then 'CHENNAI' end as CITY,count(1) as Total
from #tmptab1
group by case location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
when 7 then 'MUMBAI' when 8 then 'CHENNAI' end

对 location_id 本身进行分组也可能有效

score 1 · Accepted Answer

以下（仅通过更改您的查询 group by location_id）适用Sql-server 2008 or above（以下不确定）

select 
    case location_id 
      when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
      when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
      when 7 then 'MUMBAI' when 8 then 'CHENNAI' 
   end as CITY,
   count(*) as Total
from #tmptab1
group by location_id --NOTE

Or您可以使用

select case location_id when 1 then 'DELHI' when 2 then 'AHMEDABAD' 
            when 4 then 'HYDERABAD' when 5 then 'KOLKATA' when 6 then 'BANGALORE'
            when 7 then 'MUMBAI' when 8 then 'CHENNAI' 
            end as CITY, total
from (
    select location_id, count(*) total
    from #tmptab1 
    group by location_id ) A

sql - 按错误sql server分组

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