使用子查询中定义的列

Question

Sorry if the title is not clear, I'm a beginner and I didn't know exactly how to formule it...

I have this query working with 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

I'm looking for the equivalent for Sql Server...

The goal is to have multiple queries in a single query.

So I removed the "FROM DUAL" but I get an error on "FINANCIALOPERATIONBYPERSON" (Invalid column name), certainly because it's defined in the subquery...

How can I modify the query for SQL-Server ?

Answer 1

SQL Server requires aliases for subqueries. So, you can rewrite this as:

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;

In both databases, though, I would be inclined to write this as:

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;

One note for both these forms: SQL Server does integer arithmetic on integers. So, if AMOUNT is an integer, then you should convert it to an appropriate floating or fixed point numeric type.

Answer 2

You need to add a table alias for the subquery.

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