检查是否存在行，否则插入

我需要编写一个T-SQL存储过程来更新表中的一行。如果该行不存在，则插入它。所有这些步骤都由一个事务包装。

这是一个预订系统，所以它必须是原子和可靠的。如果事务已提交且机票已预订，则必须返回true。

我确定如何使用@@rowcount。这就是我到目前为止所写的。我走的路对吗?

-- BEGIN TRANSACTION (HOW TO DO?)
    
UPDATE Bookings
 SET TicketsBooked = TicketsBooked + @TicketsToBook
 WHERE FlightId = @Id AND TicketsMax < (TicketsBooked + @TicketsToBook)

-- Here I need to insert only if the row doesn't exists.
-- If the row exists but the condition TicketsMax is violated, I must not insert 
-- the row and return FALSE

IF @@ROWCOUNT = 0 
BEGIN

 INSERT INTO Bookings ... (omitted)
               
END

-- END TRANSACTION (HOW TO DO?)

-- Return TRUE (How to do?)

当前回答

INSERT INTO table ( column1, column2, column3 )
SELECT $column1, $column2, $column3
EXCEPT SELECT column1, column2, column3
FROM table

2015-03-27 22:45:03

其他回答

这是我最近不得不做的事情:

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[cjso_UpdateCustomerLogin]
    (
      @CustomerID AS INT,
      @UserName AS VARCHAR(25),
      @Password AS BINARY(16)
    )
AS 
    BEGIN
        IF ISNULL((SELECT CustomerID FROM tblOnline_CustomerAccount WHERE CustomerID = @CustomerID), 0) = 0
        BEGIN
            INSERT INTO [tblOnline_CustomerAccount] (
                [CustomerID],
                [UserName],
                [Password],
                [LastLogin]
            ) VALUES ( 
                /* CustomerID - int */ @CustomerID,
                /* UserName - varchar(25) */ @UserName,
                /* Password - binary(16) */ @Password,
                /* LastLogin - datetime */ NULL ) 
        END
        ELSE
        BEGIN
            UPDATE  [tblOnline_CustomerAccount]
            SET     UserName = @UserName,
                    Password = @Password
            WHERE   CustomerID = @CustomerID    
        END

    END

2009-03-12 18:23:51

我假设每个航班都有一排座位?如果是这样:

IF EXISTS (SELECT * FROM Bookings WHERE FLightID = @Id)
BEGIN
    --UPDATE HERE
END
ELSE
BEGIN
   -- INSERT HERE
END

我认为我说的，因为你的做事方式可能会超额预订航班，因为当最多有10张票而你预订了20张票时，它会插入一个新的行。

2009-03-12 18:21:41

我在写我的解。我的方法不支持“if”或“merge”。我的方法很简单。

INSERT INTO TableName (col1,col2)
SELECT @par1, @par2
   WHERE NOT EXISTS (SELECT col1,col2 FROM TableName
                     WHERE col1=@par1 AND col2=@par2)

例如:

INSERT INTO Members (username)
SELECT 'Cem'
   WHERE NOT EXISTS (SELECT username FROM Members
                     WHERE username='Cem')

解释:

(1) SELECT col1,col2 FROM TableName WHERE col1=@par1 AND col2=@par2 它从TableName搜索值中选择

(2)选择不存在的@par1， @par2 它接受(1)子查询中if不存在

(3)在TableName(2)中插入步骤值

2013-02-25 00:48:04

简单的方法将数据从T1复制到T2，避免在T2中重复

--Insert a new record
INSERT INTO dbo.Table2(NoEtu, FirstName, LastName)
SELECT t1.NoEtuDos, t1.FName, t1.LName 
FROM dbo.Table1 as t1
WHERE NOT EXISTS (SELECT (1) FROM dbo.Table2  AS t2
                    WHERE t1.FName = t2.FirstName
                        AND t1.LName = t2.LastName
                        AND t1.NoEtuDos = t2.NoEtu)

2022-01-05 22:02:48

看一下MERGE命令。你可以在一条语句中执行UPDATE, INSERT和DELETE操作。

下面是一个使用MERGE的工作实现 -在更新之前检查航班是否已满，否则执行插入操作。

if exists(select 1 from INFORMATION_SCHEMA.TABLES T 
              where T.TABLE_NAME = 'Bookings') 
begin
    drop table Bookings
end
GO

create table Bookings(
  FlightID    int identity(1, 1) primary key,
  TicketsMax    int not null,
  TicketsBooked int not null
)
GO

insert  Bookings(TicketsMax, TicketsBooked) select 1, 0
insert  Bookings(TicketsMax, TicketsBooked) select 2, 2
insert  Bookings(TicketsMax, TicketsBooked) select 3, 1
GO

select * from Bookings

然后……

declare @FlightID int = 1
declare @TicketsToBook int = 2

--; This should add a new record
merge Bookings as T
using (select @FlightID as FlightID, @TicketsToBook as TicketsToBook) as S
    on  T.FlightID = S.FlightID
      and T.TicketsMax > (T.TicketsBooked + S.TicketsToBook)
  when matched then
    update set T.TicketsBooked = T.TicketsBooked + S.TicketsToBook
  when not matched then
    insert (TicketsMax, TicketsBooked) 
    values(S.TicketsToBook, S.TicketsToBook);

select * from Bookings

2009-03-13 04:34:59

检查是否存在行，否则插入

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