SQL 获取多个连接的平均值

Question

我正在尝试使用 3 个表编写一个查询。
我将使用的表格及其列是：

Sec – ID, Symbol
Hss – Code, HDate, Holiday
Fddd – ID, Date, Price

给定一个符号AAA，我需要从第一个表中获取 ID 并将其与第三个表中的 ID 匹配。第二个表的日期必须与第三个表的日期匹配，条件为Code=1 和Holiday=1。

第二个和第三个表格中的日期按升序排列，最近的日期在底部。我想得到50 day 和200 day 的平均价格。表格中的日期按升序排列，因此我想将其降序并选择top 50 和200 以获得平均价格。

到目前为止，我只能得到一个平均值。我无法添加第二个SELECT TOP 50 或在第二个avg() 中添加subquery。

SELECT AVG(TwoHun)TwoHunAvg   --, AVG(Fifty) AS FiftyAvg 
FROM (SELECT TOP 200 Fddd.price AS TwoHun    --, TOP 50 Fddd.price AS Fifty
FROM Sec 
JOIN Fddd
ON Sec.ID = Fddd.ID AND Sec.symbol = 'AAA' 
JOIN Hss 
ON Fddd.date = Hss.Hdate AND Hss.Code = 1 AND Hss.Holiday = 1 
ORDER BY Fddd.Date DESC) AS tmp;

提前致谢！

Answer 1

考虑一个联合查询，它甚至可以扩展到其他平均值。我添加了一个类型列来指示平均值。

SELECT '200 DAY AVG' As Type, AVG(TwoHun) As Avg
FROM 
  (SELECT TOP 200 Fddd.price AS TwoHun
   FROM Sec 
   INNER JOIN Fddd ON Sec.ID = Fddd.ID 
   INNER JOIN Hss ON Fddd.date = Hss.Hdate
   WHERE Sec.symbol = 'AAA' AND Hss.Code = 1 AND Hss.Holiday = 1 
   ORDER BY Fddd.Date DESC) AS tmp;

UNION

SELECT '50 DAY AVG' As Type, AVG(FiftyHun) As Avg
FROM 
  (SELECT TOP 50 Fddd.price AS FiftyHun
   FROM Sec 
   INNER JOIN Fddd ON Sec.ID = Fddd.ID
   INNER JOIN Hss ON Fddd.date = Hss.Hdate
   WHERE Sec.symbol = 'AAA' AND Hss.Code = 1 AND Hss.Holiday = 1 
   ORDER BY Fddd.Date DESC) AS tmp;

另外，我将您的一些连接表达式移到了 where 子句中，该子句不会改变性能，但会提高可读性。

Answer 2

我怀疑您使用的是 SQL Server 或 MS Access。

一种快速的解决方案是将您的总查询作为子查询，然后复制修改后的版本作为第二个子查询。

快速粗略的例子：

    SELECT (SELECT
         AVG(Fifty) AS FiftyAvg
       FROM (SELECT TOP 50
         Fddd.price AS Fifty
       FROM Sec
       JOIN Fddd
         ON Sec.ID = Fddd.ID
         AND Sec.symbol = 'AAA'
       JOIN Hss
         ON Fddd.date = Hss.Hdate
         AND Hss.Code = 1
         AND Hss.Holiday = 1
       ORDER BY Fddd.Date DESC) AS tmp)
       AS FiftyAvg,
       (SELECT
         AVG(TwoHun) TwoHunAvg
       FROM (SELECT TOP 200
         Fddd.price AS TwoHun
       FROM Sec
       JOIN Fddd
         ON Sec.ID = Fddd.ID
         AND Sec.symbol = 'AAA'
       JOIN Hss
         ON Fddd.date = Hss.Hdate
         AND Hss.Code = 1
         AND Hss.Holiday = 1
       ORDER BY Fddd.Date DESC) AS tmp)
       AS TwoHundredAverge;