使用Switch語句和左連接訪問選擇Top 1 SQL

Question

所以我不確定我搞砸了多少Access SQL查詢，但它相當複雜。

這裏是場景：有三個表格。一個叫做「PriceMatrix」，一個叫做「PreApprovedPricing」，最後一個叫做「Request」。批准的定價包含按狀態列出的「批准」價格，「價格矩陣」包含從另一個來源生成的價格列表，請求是所有這些都指向（也包含州）的父記錄。我試圖編寫一個查詢來比較每個表格中的價格，如果預先批准的價格低於價格矩陣中的價格，它會替換字段中的值，但是如果它大於，那麼它會保留原價格矩陣價格。我試過用switch語句來查看給定的狀態。

這裏是我的查詢：

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; 

我不斷收到語法錯誤，但我似乎無法深入其中的一個問題是，從而產生。所以任何輸入都會很好，因爲我仍在學習SQL

Answer 1

您不能有多個From子句。您的發言

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; 

居然是：

Select Top 
From 
Where 
Order by 
From 
Left Join 

那一定會得到語法錯誤。我假設你想在那裏有一個子查詢。也許是這樣的（但很難說肯定）：

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;