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

Msg 207，Level 16，State 1，Line 12
列名称“CITY”
无效

如何纠正这个？请帮忙。

Answer 1

您不能在GROUP BY子句中使用列别名。请参阅Conceptual Order of Evaluation of a Select Statement，您将看到这些条款按照此顺序进行（逻辑）评估：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，但它是一个有用的启发式方法，可以实际理解为什么不能使用SELECT子句中GROUP BY语句中的内容 - - GROUP BY子句在逻辑上不可用，因为稍后会对其进行评估。

有几种解决方法：

重复GROUP BY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，您可能只需执行GROUP BY location_id，但这不是正常情况，您不应该通过选择来绕过期望能够绕过正常的聚合分组逻辑单列，因为大多数情况下这样的CASE表达式会增加不确定的值。

事实上，因为信息不仅是确定性的，而且是关于现实世界（而不是业务规则），我建议您不要在查询中对此信息进行编码！创建一个Location表并加入其中。将可更改的用户数据直接放入查询中并不是最佳做法 - 查询应该记录进程，而不是内容，以及如果添加新的location_id会怎样？使用它的所有查询都必须更改。此外，如果多个location_id可以引用同一个城市，则按location_id分组将无法正常工作。

Answer 2

您不能在group by语句中使用别名您将需要

中小组中的选择的整个部分

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

对位置ID本身进行分组也可能有效

Answer 3

关注（仅通过 group by location_id更改您的查询）适用于Sql-server 2008 or above（不确定如下）

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

按错误sql server分组

3 个答案: