EXISTS 不引入子查询时，select 列表中只能指定一个表达式。 - SQL 服务器

Question

我正在尝试创建一个存储过程，我使用 SQL 服务器编写了这段代码，但出现错误

Only one expression can be specified in the select list when the subquery is not introduced with EXISTS

不知道怎么解决

CREATE PROCEDURE Calculus
AS
BEGIN
    SELECT
        -- **** Media (Average) **** --
        (SELECT CAST(AVG(CAST(CC AS NUMERIC)) AS VARCHAR(MAX))
         FROM CHALLENGE AS Media),
        -- **** Mediana **** --
        (SELECT CASE WHEN COUNT(CC) % 2 = 0 
                THEN (SELECT TOP 1 ((SELECT TOP 1 CC 
                                     FROM (SELECT TOP 50 PERCENT CC FROM CHALLENGE ORDER  BY CC ASC) AS X
                                     ORDER  BY CC DESC)
                                  + (SELECT TOP 1 CC
                                     FROM (SELECT TOP 50 PERCENT CC FROM CHALLENGE ORDER  BY CC DESC) AS Y
                                     ORDER  BY CC ASC)) / 2)
                ELSE (SELECT TOP 1 CC
                      FROM (SELECT TOP 50 PERCENT CC FROM CHALLENGE ORDER  BY CC) AS X
                      ORDER  BY CC DESC)
                END AS Mediana
         FROM   CHALLENGE),
        -- **** Moda **** --
        (SELECT TOP 1 CC, COUNT(CC) AS Veces
         FROM CHALLENGE
         GROUP BY CC
         ORDER BY COUNT(CC)) AS Moda,
        -- **** Min **** --
        MIN(CC) AS Minimo,
        -- **** Max **** --
        MAX(CC) AS Maximo
    FROM
        CHALLENGE
END

Answer 1

为了清晰起见，您应该从重构存储过程开始。

下面的示例供参考

CREATE PROCEDURE Calculus
AS
  BEGIN
      DECLARE @Media varchar(max)
      DECLARE @Mediana varchar(max)
      DECLARE @topbottom numeric
      DECLARE @bottomtop numeric
      DECLARE @Moda varchar(max)
      SELECT 
            @Media= Cast(Avg(Cast (CC AS numeric)) AS varchar(max))
      FROM CHALLENGE

      SELECT 
        TOP 50 PERCENT CC 
      INTO #TOP
      FROM   CHALLENGE
      ORDER  BY CC ASC

      SELECT 
        TOP 50 PERCENT CC 
      INTO #BOTTOM
      FROM   CHALLENGE
      ORDER  BY CC DESC

      SELECT 
            TOP 1 @topbottom=CAST(CC as numeric)
      FROM   #TOP X
      ORDER  BY CC DESC 

      SELECT 
        TOP 1 @bottomtop=CAST(CC as numeric)
       FROM   #BOTTOM Y
       ORDER  BY CC ASC

      SELECT @Mediana=
            CASE
                WHEN Count(CC) % 2 = 0 THEN (@bottomtop+@topbottom)/2
                ELSE @topbottom
              END 
       FROM   CHALLENGE

      SELECT TOP 1 
        @Moda= CC
        FROM
      (
      SELECT CC,Count(CC) AS Veces
       FROM   CHALLENGE
       GROUP  BY CC
       )
       ORDER  BY Veces


      SELECT
        Media=@Media,
        Mediana=@Mediana,
        Moda= @Moda,
        Minimo=Min(CC),
        Maximo=Max(CC)
      FROM   CHALLENGE

      drop table #top
      drop table #bottom
  END

Answer 2

这部分查询导致错误。

这是一个子查询，您正在尝试从中 return 2 列（这会导致错误）。

TOP 1 CC 和 COUNT(CC)

(SELECT TOP 1 CC
       ,COUNT(CC) AS Veces
 FROM CHALLENGE
 GROUP BY CC
 ORDER BY COUNT(CC)) AS Moda

不确定要建议什么，因为您肯定是唯一知道您打算从这里得到什么的人。

Answer 3

您应该更改查询并将每个子查询放入（OUTER APPLY）join

像这样：

   CREATE PROCEDURE Calculus
    AS
    BEGIN
        SELECT
              MediaTableName.MediaFieldName

        FROM
            CHALLENGE
        OUTER APPLY 
            (SELECT CAST(AVG(CAST(CC AS NUMERIC)) AS VARCHAR(MAX)) as MediaFieldName
             FROM CHALLENGE AS t1
             WHERE t1.IDentity = CHALLENGE.IDentity /* this line create join condition and its up to you how use it*/
             ) as MediaTableName

    END

对于每个子查询使用一个外部 aplly 连接您可以删除 where 子句行

EXISTS 不引入子查询时，select 列表中只能指定一个表达式。 - SQL 服务器

Only one expression can be specified in the select list when the subquery is not introduced with EXISTS. - SQL Server

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