访问数据库查询：计算价格变化

Question

我尝试使用以下SQL创建查询以计算订单历史记录表中的价格变化。 Access给我一个警告＆＃34;最多可以返回一条记录......＆＃34;它用＆＃34; #Name？＆＃34;返回了一条记录在每个领域。有人可以帮我解决这个问题吗？非常感谢。

SELECT History.PartNumber,History.Datetime, History.Price, History.Quantity, (SELECT TOP 1 Price FROM History AS History1 
WHERE History1.Datetime < History.Datetime 
AND History1.PartNumber = History.PartNumber ORDER BY History1.Datetime DESC) as PreviousPrice, 
[PreviousPrice]-[Price] as PriceDiff
FROM History
ORDER BY History.PartNumber, History.Datetime DESC

我测试了以下代码作为查询的子集，并收到以下错误： Error dialog box 点击OK按钮后，我得到了这个： #Name? in all fields

SELECT 
history.partnumber, 
history.datetime, 
history.price, 
history.quantity, 
(SELECT TOP 1 price 
  FROM   history AS History1 
  WHERE  History1.datetime < history.datetime 
AND History1.partnumber = history.partnumber 
  ORDER  BY History1.datetime DESC
 ) AS PreviousPrice
FROM history

Answer 1

您无法在 list<string> mylist = new list<string>; foreach(string item in mylist) { ///To get letters/alphabets var letters = new String(item.Where(Char.IsLetter).ToArray()); ///to get special characters var letters = new String(item.Where(Char.IsSymbol).ToArray()) } 上计算价格变化，因为PreviousPrice是PreviousPrice子查询上的别名

使用子查询制作select列

您可以尝试此查询。

PreviousPrice

如果不包含SELECT t.*, (t.previousprice - t.price) AS PriceDiff FROM ( SELECT history.partnumber, history.datetime, history.price, history.quantity, ( SELECT TOP 1 price FROM history AS History1 WHERE History1.datetime < history.datetime AND History1.partnumber = history.partnumber ORDER BY History1.datetime DESC ) AS PreviousPrice FROM history )t ORDER BY t.partnumber, t.datetime DESC ，我认为你需要使用coalesce函数。

PreviousPrice

sqlfiddle：http://sqlfiddle.com/#!18/52a7b/5

修改

在我的访问中，此查询效果很好。

如果您想在 SELECT t.partnumber, t.datetime, t.price, t.quantity, coalesce(t.PreviousPrice,0) as 'PreviousPrice', coalesce((t.previousprice - t.price),0) AS 'PriceDiff' FROM ( SELECT history.partnumber, history.datetime, history.price, history.quantity, ( SELECT TOP 1 price FROM history AS History1 WHERE History1.datetime < history.datetime AND History1.partnumber = history.partnumber ORDER BY History1.datetime DESC ) AS PreviousPrice FROM history )t ORDER BY t.partnumber, t.datetime DESC 列添加货币符号，可以使用Format功能。

你可以试试这个。

PriceDiff

来源数据

查询结果

sqlfiddle：http://sqlfiddle.com/#!18/bfddb/6

修改＃2

我看到了您的源数据，源数据中有许多重复的SELECT t.*, abs(t.previousprice - t.price) AS PriceDiff FROM ( SELECT history.partnumber, history.datetime, history.price, history.quantity, ( SELECT TOP 1 price FROM history AS History1 WHERE History1.datetime < history.datetime AND History1.partnumber = history.partnumber ORDER BY History1.datetime DESC ) AS PreviousPrice FROM history )t WHERE t.PreviousPrice is not null ORDER BY t.partnumber, t.datetime 。您不能在子查询上使用datetime进行比较，否则子查询中会有多行。

因此您可以与datetime列进行比较，因为它是您的ID。

您可以使用PK代替ID

datetime

sqlfiddle：http://sqlfiddle.com/#!18/bdeb91/1