Question

是否可以在以下声明中为'a','b','test','123','blabla'创建一些启示？

sum(case when col1 in ('a','b','test','123','blabla') then col2 end) as sum

我试图从letters_table这样读取它：

sum(case when col1 in (select letter from letters_table) then col2 end) as sum

但它告诉我Cannot perform an aggregate function on an expression containing an aggregate or a subquery.

以下对我不起作用：

DECLARE @letters varchar(10)
select @letters = letter FROM letters_table
sum(case when col1 in (@letters) then col2 end) as sum

因为当我打印@letters时，只有最后一个'blabla'

Answer 1

如果表格中有col1（文本列）和col2（数字列），请说myTable和另一个表中的字母（文本列），比如letters_table，那么你可以使用JOIN，如下所示：

SELECT 
    --mt.col1,        Include for totals by col1
    SUM(mt.col2)
FROM myTable mt
INNER JOIN letters_table lt
ON mt.col1 = lt.letter;
--    GROUP BY mt.col1    Include for totals by col1
--    ORDER BY mt.col1;   Include for totals by col1

Answer 2

使用子查询的第二个示例可能是最好的 - 您只需要在两个单独的阶段中执行子查询和聚合，如下所示：

select sum(x.col2) as sum
from (
    select case 
           when col1 in (select letter from letters_table) then col2 
           else 0 
           end as col2
    from YourTableName
) x

这应该按预期工作，并使解析器满意。

Answer 3

...或者您可以使用公用表表达式，例如：

DECLARE @Test TABLE (col1 VARCHAR(1), col2 INT);
INSERT INTO @Test VALUES ('a', 1);
INSERT INTO @Test VALUES ('c', 20);
INSERT INTO @Test VALUES ('z', 3);
DECLARE @Letters TABLE (Letter VARCHAR(1));
INSERT INTO @Letters VALUES ('a');
INSERT INTO @Letters VALUES ('b');
INSERT INTO @Letters VALUES ('c');
WITH PreQuery AS (
    SELECT
        col1,
        CASE WHEN l.Letter IS NULL THEN 0 ELSE 1 END AS GoodLetter,
        col2
    FROM
        @Test t
        LEFT JOIN @Letters l ON l.Letter = t.col1)
SELECT 
    SUM(CASE WHEN GoodLetter = 1 THEN col2 END) 
FROM 
    PreQuery;

Answer 4

solution posted by Richard应该可以解决问题，但不需要使用cte 你可以简单地使用下面的代码

select
   isnull(sum(mt.col2),0)
from 
  myTbl mt
  inner join lettersTbl lt
    on mt.col1 = lt.letter

如果要包含结果中涉及的字母，可以使用变量。在这里查看your previous post是一个代码，其中包含您提供的相同示例数据

declare @yourTbl table (col1 char(1), col2 int);
insert into @yourTbl values ('a', 10)
,('b', 5)
,('c', 15)
,('d', 2)
,('a', 3)
,('b', 6) 
,('c', 8) 
,('d', 10);

declare @lettersTbl table (letter char(1));
-- insert your letters here
insert into @lettersTbl values ('a'),('b')


-- only needed if you want to display the letters involved too
declare @checkedLetters as varchar(50)
select @checkedLetters = concat(@checkedletters,lt.letter)
from 
    @letterstbl lt

select
    @checkedletters 
   ,isnull(sum(mt.col2),0)
from 
    @yourtbl mt
    inner join @letterstbl lt
      on mt.col1 = lt.letter

创建枚举并在聚合函数中使用它

4 个答案: