Question

我想从3个表及其行中提取数据，如下所示：
**RentalAgreement – CustID,AgreementID(PK) and AgreementDate **Movie Rented – AgreementID(PK), RentalAmount and PercentReductionApplied,MovieID(FK) **Movie – MovieID(PK), Name, Released

我需要根据表格而不是当前数据显示过去30天的数据。我怎样才能实现这一目标？我的尝试：

SELECT TRIM(CustID),AgreementDate , RentalAmount    
             ,PercentReductionApplied , MovieID , Name , Released
FROM RentalAgreement, MovieRented, Movie
WHERE RentalAgreement.AgreementID = MovieRented.AgreementID
AND Movie.MovieID = MovieRented.MovieID
AND AgreementDate BETWEEN MAX(AgreementDate) AND MAX(AgreementDate)-30;

Answer 1

问题在于MAX（协议日期）。这是一个聚合函数 - 在处理WHERE子句之后，您只能在查询的最后一个阶段（在SELECT子句中）访问它。这意味着您需要一个不同的查询来首先计算MAX - 并将其用作整体（外部）查询中的子查询。

最好使用现代的SQL标准连接语法。将这两者放在一起：

SELECT TRIM(CustID),AgreementDate , RentalAmount    
             ,PercentReductionApplied , MovieID , Name , Released
FROM RentalAgreement
     join MovieRented on RentalAgreement.AgreementID = MovieRented.AgreementID
     join Movie       on Movie.MovieID               = MovieRented.MovieID
     cross join (select max(agreementdate) as max_date from rentalagreement) m
where AgreementDate BETWEEN m.max_date AND m.max_date - 30;

为什么需要TRIM（custID）？这很不寻常。同样奇怪的是，ProtocolID是MovieRented中的PRIMARY键。但这些并不是您的查询无效的原因。

Answer 2

DECLARE @StartDate DATETIME，@ EndDate DATETIME

SELECT @StartDate = MAX（AgreementDate）FROM RentalAgreement SET @EndDate = DATEADD（DAY，-30，@ StartDate）

SELECT TRIM（CustID），AgreementDate，RentalAmount
，PercentReductionApplied，MovieID，Name，已发布来自RentalAgreement，MovieRented，电影 WHERE RentalAgreement.AgreementID = MovieRented.AgreementID AND Movie.MovieID = MovieRented.MovieID 与@StartDate和@EndDate之间的协议日期

根据表数据而非当前日期获取可显示30天的查询

2 个答案: