检查行是否存在，否则插入

Question

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。所有这些步骤都包含在事务中。

这是一个预订系统，因此它必须是“原子且可靠的”。如果交易已提交且航班已预订，则它必须返回 true。 我确定如何使用

@@rowcount

。这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?)

Answer 1

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

我假设我所说的，因为你的做法可能会超额预订航班，因为当最多 10 张机票而你预订 20 张机票时，它会插入一个新行。

Answer 2

MERGE 命令。您可以在一条语句中执行 UPDATE、

INSERT

和

DELETE

。这是使用

MERGE

 的工作实现
- 在进行更新之前检查航班是否已满，否则进行插入。

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

Answer 3

begin tran /* default read committed isolation level is fine */

if not exists (select * from Table with (updlock, rowlock, holdlock) where ...)
    /* insert */
else
    /* update */

commit /* locks are released here */

updlock 提示强制查询在该行已存在时获取更新锁，以防止其他事务修改它，直到您提交或回滚。

holdlock 提示强制查询采用范围锁，防止其他事务添加与您的过滤条件匹配的行，直到您提交或回滚。

行锁提示强制锁定粒度为行级别而不是默认页面级别，因此您的事务不会阻止尝试更新同一页面中不相关行的其他事务（但要注意减少争用和增加争用之间的权衡）在锁定开销中 - 您应该避免在单个事务中获取大量行级锁）。

请参阅

http://msdn.microsoft.com/en-us/library/ms187373.aspx

了解更多信息。 请注意，锁被视为执行获取它们的语句 - 调用 begin tran 并不能让您免受另一个事务在您到达某事物之前夹住锁的影响。 您应该尝试并考虑您的 SQL，通过尽快提交事务（晚获取，早释放）来尽可能短地持有锁。

请注意，如果您的 PK 是 bigint，行级锁的效果可能会较差，因为 SQL Server 上的内部哈希对于 64 位值来说是退化的（不同的键值可能会哈希到相同的锁 ID）。

Answer 4

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')

说明：

(1) 从表名中选择 col1,col2，其中 col1=@par1 AND col2=@par2 它从 TableName 搜索值中选择

(2) 在不存在的情况下选择@par1、@par2 如果不存在则需要 (1) 子查询

(3) 插入 TableName (2) 步骤值

Answer 5

INSERT INTO table ( column1, column2, column3 )
(
    SELECT $column1, $column2, $column3
      WHERE NOT EXISTS (
        SELECT 1
          FROM table 
          WHERE column1 = $column1
          AND column2 = $column2
          AND column3 = $column3 
    )
)

我发现于：

http://www.postgresql.org/message-id/

[电子邮件受保护]

Answer 6

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

Answer 7

合并

功能来实现。否则你可以这样做：

declare @rowCount int

select @rowCount=@@RowCount

if @rowCount=0
begin
--insert....

Answer 8

begin trans ... commit

代码。

declare @mystat6 bigint
declare @mystat6p varchar(50)
declare @mystat6b bigint

DECLARE mycur1 CURSOR for

 select result1,picture,bittot from  all_Tempnogos2results11

 OPEN mycur1

 FETCH NEXT FROM mycur1 INTO @mystat6, @mystat6p , @mystat6b

 WHILE @@Fetch_Status = 0
 BEGIN

 begin tran /* default read committed isolation level is fine */

 if not exists (select * from all_Tempnogos2results11_uniq with (updlock, rowlock, holdlock)
                     where all_Tempnogos2results11_uniq.result1 = @mystat6 
                        and all_Tempnogos2results11_uniq.bittot = @mystat6b )
     insert all_Tempnogos2results11_uniq values (@mystat6 , @mystat6p , @mystat6b)

 --else
 --  /* update */

 commit /* locks are released here */

 FETCH NEXT FROM mycur1 INTO @mystat6 , @mystat6p , @mystat6b

 END

 CLOSE mycur1

 DEALLOCATE mycur1
 go

Answer 9

Answer 10

--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)

Answer 11

Answer 12

ALTER TABLE table_name ADD UNIQUE KEY

THEN INSERT IGNORE INTO table_name

，如果导致重复键/表中已存在该值，则不会插入该值。