使用子查詢中定義的列

Question

抱歉，標題不清楚，我是初學者，我不知道該如何制定...

我有這個查詢使用Oracle：

SELECT

   ( SELECT COUNT(*)
     FROM   CATEGORY
   ) AS NBCATEGORIES,

   ( SELECT ROUND(AVG(FINANCIALOPERATIONBYPERSON),2)
    FROM
         (
            SELECT SUM(AMOUNT) AS FINANCIALOPERATIONBYPERSON
            FROM FINANCIALOPERATION
            WHERE PERSONID IS NOT NULL
            GROUP BY PERSONID
         )
     ) AS AVERAGELOADAMOUNTBYPERSON

FROM DUAL

我正在尋找等效的Sql Server ...

目標是在一個查詢中包含多個查詢。

因此，我刪除了“ FROM DUAL”，但由於“ FINANCIALOPERATIONBYPERSON”（無效的列名）而出現錯誤，肯定是因為它是在子查詢中定義的...

如何修改SQL-Server的查詢？

Answer 1

SQL Server要求子查詢使用別名。 因此，您可以將其重寫為：

SELECT (SELECT COUNT(*)
        FROM   CATEGORY
       ) AS NBCATEGORIES,
       (SELECT ROUND(AVG(FINANCIALOPERATIONBYPERSON),2)
        FROM (SELECT SUM(AMOUNT) AS FINANCIALOPERATIONBYPERSON
              FROM FINANCIALOPERATION
              WHERE PERSONID IS NOT NULL
              GROUP BY PERSONID
             ) t
       ) AS AVERAGELOADAMOUNTBYPERSON;

但是，在這兩個數據庫中，我傾向於將其編寫為：

SELECT c.NBCATEGORIES, ROUND(fo.AVERAGELOADAMOUNTBYPERSON, 2) AS AVERAGELOADAMOUNTBYPERSON
FROM (SELECT COUNT(*) as NBCATEGORIES
      FROM CATEGORY c
     ) c CROSS JOIN
     (SELECT SUM(AMOUNT) / COUNT(DISTINCT PERSONID) AS AVERAGELOADAMOUNTBYPERSON
      FROM FINANCIALOPERATION fo
      WHERE PERSONID IS NOT NULL
     ) fo;

這兩種形式的一個注意事項：SQL Server對整數執行整數算術。 因此，如果AMOUNT是整數，則應將其轉換為適當的浮點或定點數字類型。

Answer 2

您需要為子查詢添加表別名。

SELECT
( SELECT COUNT(*)
     FROM   CATEGORY
   ) AS NBCATEGORIES,

   ( SELECT ROUND(AVG(RESULTS.FINANCIALOPERATIONBYPERSON),2)
    FROM
         (
            SELECT SUM(AMOUNT) AS FINANCIALOPERATIONBYPERSON
            FROM FINANCIALOPERATION
            WHERE PERSONID IS NOT NULL
            GROUP BY PERSONID
         ) RESULTS
     ) AS AVERAGELOADAMOUNTBYPERSON