使用 Switch 语句和左连接 Access SQL 选择 Top 1

Question

所以我不确定我把这个 Access SQL 查询搞砸了多少，但它相当复杂。

场景如下：有三个表。一种称为“PriceMatrix”，一种称为“PreApprovedPricing”，最后一种称为“Request”。已批准的定价包含按州列出的“已批准”价格列表，“价格矩阵”包含从另一个来源生成的价格列表，请求是所有这些都指向的父记录（也包含州）。我正在尝试编写一个查询来比较每个表中的价格，如果预先批准的价格小于价格矩阵中的价格，它会替换字段中的值，但如果大于，则保留原价矩阵价格。我尝试使用 switch 语句来查看给定的状态。

这是我的查询：

SELECT TOP 1 [ApprovedPrice] from [PreApprovedPricing] AS [1stMonthApproved] WHERE [ApprovedPrice] >= [PriceMatrix].[1stMonth]
ORDER BY [ApprovedPrice] ASC,
SWITCH( Request.[state] = 'CT' , [1stMonthApproved], Request.[state] = 'MA' , [1stMonthApproved], 1=1 ,  [PriceMatrix].[1stMonth]) AS 1stMonth,
FROM PriceMatrix LEFT JOIN Request ON PriceMatrix.RequestID = Request.RequestID;

我不断收到语法错误，但我似乎无法深入了解问题的根源。所以任何输入都会很棒，因为我还在学习 SQL

Answer 1

您不能有多个 From 子句。你的陈述

SELECT TOP 1 [ApprovedPrice] 
from [PreApprovedPricing] AS [1stMonthApproved] 
WHERE [ApprovedPrice] >= [PriceMatrix].[1stMonth]
ORDER BY [ApprovedPrice] ASC,
SWITCH( Request.[state] = 'CT' , [1stMonthApproved], Request.[state] = 'MA' , [1stMonthApproved], 1=1 ,  [PriceMatrix].[1stMonth]) AS 1stMonth,
FROM PriceMatrix 
LEFT JOIN Request ON PriceMatrix.RequestID = Request.RequestID;

其实是：

Select Top
From
Where
Order by
From
Left Join

那肯定会出现语法错误。我假设您想要在某个地方进行子查询。也许像这样（但很难确定）：

SELECT [ApprovedPrice] ,
    (Select top 1 SWITCH( Request.[state] = 'CT' , [1stMonthApproved], Request.[state] = 'MA' , [1stMonthApproved], 1=1 ,  [PriceMatrix].[1stMonth])
    from [PreApprovedPricing] AS [1stMonthApproved] 
    WHERE [ApprovedPrice] >= [PriceMatrix].[1stMonth]
    ORDER BY [ApprovedPrice] ASC,
        SWITCH( Request.[state] = 'CT' , [1stMonthApproved], Request.[state] = 'MA' , [1stMonthApproved], 1=1 ,  [PriceMatrix].[1stMonth])) AS 1stMonth
FROM PriceMatrix 
LEFT JOIN Request ON PriceMatrix.RequestID = Request.RequestID;