防止 SQL 中的重复预订

Question

我被困在这个问题上，我想防止重复预订的发生。这是我一直在使用的代码：

USE INL5
GO

SET ANSI_NULLS ON 
GO 

SET QUOTED_IDENTIFIER ON 
GO 

ALTER TRIGGER [dbo].[trg_bookinginfo_doublebooking] ON [dbo].[bookinginfo] 
FOR INSERT AS 
DECLARE @startdate AS DATE 
DECLARE @enddate AS DATE 
DECLARE @roomnumber AS CHAR(3) 

SELECT @startdate = inserted.startdate, @enddate = inserted.enddate, @roomnumber = inserted.roomnumber 
FROM inserted, bookinginfo 
WHERE @roomnumber = bookinginfo.roomnumber AND (@startdate BETWEEN bookinginfo.startdate AND bookinginfo.enddate) AND (@enddate BETWEEN bookinginfo.startdate AND bookinginfo.enddate) 
IF EXISTS(SELECT * FROM inserted) 

BEGIN RAISERROR ('Double bookings are not allowed',16,1) 
ROLLBACK TRANSACTION 
END

问题是无论日期是否重叠都会发生错误。我做错了什么？

Answer 1

就是因为最后那个IF EXISTS(SELECT * FROM inserted)。您不检查所选值之前，而是检查每个插入的值。它总是 return 你的东西。

它应该是这样的：

USE INL5
GO

SET ANSI_NULLS ON 
GO 

SET QUOTED_IDENTIFIER ON 
GO 

ALTER TRIGGER [dbo].[trg_bookinginfo_doublebooking] ON [dbo].[bookinginfo] 
FOR INSERT AS 
DECLARE @startdate AS DATE 
DECLARE @enddate AS DATE 
DECLARE @roomnumber AS CHAR(3) 

IF EXISTS(SELECT @startdate = inserted.startdate, @enddate = inserted.enddate, @roomnumber = inserted.roomnumber 
FROM inserted, bookinginfo 
WHERE @roomnumber = bookinginfo.roomnumber AND (@startdate BETWEEN bookinginfo.startdate AND bookinginfo.enddate) AND (@enddate BETWEEN bookinginfo.startdate AND bookinginfo.enddate) ) 

BEGIN RAISERROR ('Double bookings are not allowed',16,1) 
ROLLBACK TRANSACTION 
END

Answer 2

这条语句：

SELECT @startdate = inserted.startdate, @enddate = inserted.enddate, 
       @roomnumber = inserted.roomnumber 
FROM inserted, bookinginfo 
WHERE @roomnumber = bookinginfo.roomnumber AND
     (@startdate BETWEEN bookinginfo.startdate AND bookinginfo.enddate) AND 
     (@enddate BETWEEN bookinginfo.startdate AND bookinginfo.enddate)

高度怀疑。您在 select 中分配变量并在 where 中使用相同的变量。将其表达为正常 join 有问题吗？

SELECT @startdate = i.startdate, @enddate = i.enddate, @roomnumber = i.roomnumber 
FROM inserted i JOIN
     bookinginfo bi
     ON i.roomnumber = bi.roomnumber AND
        (i.startdate BETWEEN bi.startdate AND bi.enddate) AND 
        (i.enddate BETWEEN bi.startdate AND bi.enddate) AND
        i.BookinginfoID <> bi.BookinginfoID;

由于两个原因，这仍然不能满足您的要求。首先，这个逻辑是不正确的。第二，if 甚至没有使用它。我认为以下是您想要的触发器主体：

IF (EXISTS (SELECT 1
            FROM inserted i JOIN
                 bookinginfo bi
                 ON i.roomnumber = bi.roomnumber AND
                    i.startdate <= bi.enddate AND 
                    i.enddate >= bi.startdate AND
                    i.BookinginfoID <> bi.BookinginfoID;
           )
BEGIN
     RAISERROR ('Double bookings are not allowed',16,1)
     . . . 
END;

防止 SQL 中的重复预订

Preventing double bookings in SQL

sql

tsql

sql-server