Sql 如何从内部查询在外部查询中执行算术运算

我是SQL新手，正在尝试在access中构建查询。我需要选择比平均比率小的两列的比率。 我能够首先对数据进行分组，以获得每列的总数。我还能够在以下查询中获得每个组的比率，该查询有效：

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

但是，我只想显示那些小于平均比率的比率。我尝试了另一种方法，得到了一条消息：不能在WHERE子句中聚合函数

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)

---

谁能帮我看看我做错了什么，我已经为此工作了几个小时，老实说，我在这里不知所措。

这是Access中一个痛苦的问题。您可以这样做：

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
              );

---

谢谢你，戈登，成功了！我可以使用HAVING子句来构建这个查询吗？再次感谢！

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;