如何在內部查詢的外部查詢中執行算術運算

Question

我是SQL新手，我試圖在訪問中構建查詢。我需要選擇比平均比率小的兩列比例。 我能夠首先對數據進行分組，以便能夠獲得每列的總數。我還能夠獲得以下（查詢其作品），每組比例：

SELECT col1, Ratio 
FROM (
    SELECT ID, SUM(col3)/SUM(col4) AS Ratio 
    FROM table1 
    GROUP BY ID 
) AS Ratios 
INNER JOIN table2 
ON Ratios.ID=table2.ID 

不過，我想只顯示那些低於平均比例較小的比例。我試了一下這個別的辦法了，我得到一個消息：「能在沒有聚合函數WHERE子句」

SELECT col1, Ratio 
FROM (
    SELECT ID, SUM(col3)/SUM(col4) AS Ratio 
    FROM table1 
    GROUP BY ID 
) AS Ratios 
INNER JOIN table2 
ON Ratios.ID=table2.ID 
WHERE Ratio<AVG(Ratio) 

誰能幫我看看有什麼我做錯了，我一直在這几几小時，老實說，我在這裏虧本。

Answer 1

這是Access中的一個痛苦的查詢。你可以這樣說：

SELECT col1, Ratio 
FROM (SELECT ID, SUM(col3)/SUM(col4) AS Ratio 
     FROM table1 
     GROUP BY ID 
    ) AS Ratios INNER JOIN 
    table2 
    ON Ratios.ID = table2.ID 
WHERE Ratio < (select AVG(Ratio) 
       from (SELECT ID, SUM(col3)/SUM(col4) AS Ratio 
        FROM table1 
        GROUP BY ID 
        ) as t 
      ); 

編輯：

是的，你可以這樣做有having條款，但它必須被嵌入在子查詢：

SELECT col1, Ratio 
FROM (SELECT ID, SUM(col3)/SUM(col4) AS Ratio 
     FROM table1 
     GROUP BY ID 
     HAVING SUM(col3)/SUM(col4) < (select AVG(Ratio) 
            from (SELECT ID, SUM(col3)/SUM(col4) AS Ratio 
              FROM table1 
              GROUP BY ID 
             ) as t 
            ) 
    ) AS Ratios INNER JOIN 
    table2 
    ON Ratios.ID = table2.ID;