好的，所以我正在尝试改进我的asp数据输入页面，以确保进入我的数据表的条目是唯一的。
所以在这个表中我有SoftwareName和SoftwareType。我试图得到它，如果条目页发送一个插入查询，其参数与表中的whats匹配（所以标题和类型相同），则会抛出错误并且不输入数据。
这样的事情：
INSERT INTO tblSoftwareTitles(
SoftwareName,
SoftwareSystemType)
VALUES(@SoftwareName,@SoftwareType)
WHERE NOT EXISTS (SELECT SoftwareName
FROM tblSoftwareTitles
WHERE Softwarename = @SoftwareName
AND SoftwareType = @Softwaretype)
因此，这种语法非常适合从一个表中选择列到另一个表而不输入重复项但似乎不想使用参数化插入查询。任何人都可以帮我解决这个问题吗？
编辑：
这是我在ASP插入方法中使用的代码
private void ExecuteInsert(string name, string type)
{
//Creates a new connection using the HWM string
using (SqlConnection HWM = new SqlConnection(GetConnectionStringHWM()))
{
//Creates a sql string with parameters
string sql = " INSERT INTO tblSoftwareTitles( "
+ " SoftwareName, "
+ " SoftwareSystemType) "
+ " SELECT "
+ " @SoftwareName, "
+ " @SoftwareType "
+ " WHERE NOT EXISTS "
+ " ( SELECT 1 "
+ " FROM tblSoftwareTitles "
+ " WHERE Softwarename = @SoftwareName "
+ " AND SoftwareSystemType = @Softwaretype); ";
//Opens the connection
HWM.Open();
try
{
//Creates a Sql command
using (SqlCommand addSoftware = new SqlCommand{
CommandType = CommandType.Text,
Connection = HWM,
CommandTimeout = 300,
CommandText = sql})
{
//adds parameters to the Sql command
addSoftware.Parameters.Add("@SoftwareName", SqlDbType.NVarChar, 200).Value = name;
addSoftware.Parameters.Add("@SoftwareType", SqlDbType.Int).Value = type;
//Executes the Sql
addSoftware.ExecuteNonQuery();
}
Alert.Show("Software title saved!");
}
catch (System.Data.SqlClient.SqlException ex)
{
string msg = "Insert Error:";
msg += ex.Message;
throw new Exception(msg);
}
}
}
答案 0 :(得分：58)
我会使用和IF声明：
IF NOT EXISTS
( SELECT 1
FROM tblSoftwareTitles
WHERE Softwarename = @SoftwareName
AND SoftwareSystemType = @Softwaretype
)
BEGIN
INSERT tblSoftwareTitles (SoftwareName, SoftwareSystemType)
VALUES (@SoftwareName, @SoftwareType)
END;
您可以在IF使用SELECT
INSERT tblSoftwareTitles (SoftwareName, SoftwareSystemType)
SELECT @SoftwareName,@SoftwareType
WHERE NOT EXISTS
( SELECT 1
FROM tblSoftwareTitles
WHERE Softwarename = @SoftwareName
AND SoftwareSystemType = @Softwaretype
);
这两种方法都容易受到race condition的影响，所以虽然我仍然会使用上述方法之一进行插入，但是您可以使用唯一约束来保护重复插入：
CREATE UNIQUE NONCLUSTERED INDEX UQ_tblSoftwareTitles_Softwarename_SoftwareSystemType
ON tblSoftwareTitles (SoftwareName, SoftwareSystemType);
<强>附录
在SQL Server 2008或更高版本中，您可以将MERGE与HOLDLOCK一起使用，以消除竞争条件的可能性（仍然不能替代唯一约束）。
MERGE tblSoftwareTitles WITH (HOLDLOCK) AS t
USING (VALUES (@SoftwareName, @SoftwareType)) AS s (SoftwareName, SoftwareSystemType)
ON s.Softwarename = t.SoftwareName
AND s.SoftwareSystemType = t.SoftwareSystemType
WHEN NOT MATCHED BY TARGET THEN
INSERT (SoftwareName, SoftwareSystemType)
VALUES (s.SoftwareName, s.SoftwareSystemType);
答案 1 :(得分：7)
这不是答案。我只想表明IF NOT EXISTS(...) INSERT方法不安全。您必须先执行Session #1然后Session #2。在v #2之后，您会看到如果没有UNIQUE索引，您可能会获得重复的对(SoftwareName,SoftwareSystemType)。会话＃1的延迟用于为您提供足够的时间来执行第二个脚本（会话＃2）。你可以减少这种延迟。
会话＃1 （SSMS＆gt;新查询＆gt; F5（执行））
CREATE DATABASE DemoEXISTS;
GO
USE DemoEXISTS;
GO
CREATE TABLE dbo.Software(
SoftwareID INT PRIMARY KEY,
SoftwareName NCHAR(400) NOT NULL,
SoftwareSystemType NVARCHAR(50) NOT NULL
);
GO
INSERT INTO dbo.Software(SoftwareID,SoftwareName,SoftwareSystemType)
VALUES (1,'Dynamics AX 2009','ERP');
INSERT INTO dbo.Software(SoftwareID,SoftwareName,SoftwareSystemType)
VALUES (2,'Dynamics NAV 2009','SCM');
INSERT INTO dbo.Software(SoftwareID,SoftwareName,SoftwareSystemType)
VALUES (3,'Dynamics CRM 2011','CRM');
INSERT INTO dbo.Software(SoftwareID,SoftwareName,SoftwareSystemType)
VALUES (4,'Dynamics CRM 2013','CRM');
INSERT INTO dbo.Software(SoftwareID,SoftwareName,SoftwareSystemType)
VALUES (5,'Dynamics CRM 2015','CRM');
GO
/*
CREATE UNIQUE INDEX IUN_Software_SoftwareName_SoftareSystemType
ON dbo.Software(SoftwareName,SoftwareSystemType);
GO
*/
-- Session #1
BEGIN TRANSACTION;
UPDATE dbo.Software
SET SoftwareName='Dynamics CRM',
SoftwareSystemType='CRM'
WHERE SoftwareID=5;
WAITFOR DELAY '00:00:15' -- 15 seconds delay; you have less than 15 seconds to switch SSMS window to session #2
UPDATE dbo.Software
SET SoftwareName='Dynamics AX',
SoftwareSystemType='ERP'
WHERE SoftwareID=1;
COMMIT
--ROLLBACK
PRINT 'Session #1 results:';
SELECT *
FROM dbo.Software;
会话＃2 （SSMS＆gt;新查询＆gt; F5（执行））
USE DemoEXISTS;
GO
-- Session #2
DECLARE
@SoftwareName NVARCHAR(100),
@SoftwareSystemType NVARCHAR(50);
SELECT
@SoftwareName=N'Dynamics AX',
@SoftwareSystemType=N'ERP';
PRINT 'Session #2 results:';
IF NOT EXISTS(SELECT *
FROM dbo.Software s
WHERE s.SoftwareName=@SoftwareName
AND s.SoftwareSystemType=@SoftwareSystemType)
BEGIN
PRINT 'Session #2: INSERT';
INSERT INTO dbo.Software(SoftwareID,SoftwareName,SoftwareSystemType)
VALUES (6,@SoftwareName,@SoftwareSystemType);
END
PRINT 'Session #2: FINISH';
SELECT *
FROM dbo.Software;
结果：
Session #1 results:
SoftwareID SoftwareName SoftwareSystemType
----------- ----------------- ------------------
1 Dynamics AX ERP
2 Dynamics NAV 2009 SCM
3 Dynamics CRM 2011 CRM
4 Dynamics CRM 2013 CRM
5 Dynamics CRM CRM
Session #2 results:
Session #2: INSERT
Session #2: FINISH
SoftwareID SoftwareName SoftwareSystemType
----------- ----------------- ------------------
1 Dynamics AX ERP <-- duplicate (row updated by session #1)
2 Dynamics NAV 2009 SCM
3 Dynamics CRM 2011 CRM
4 Dynamics CRM 2013 CRM
5 Dynamics CRM CRM
6 Dynamics AX ERP <-- duplicate (row inserted by session #2)
答案 2 :(得分：6)
这个问题有一个很好的解决方案，您可以使用Sql的合并关键字
Merge MyTargetTable hba
USING (SELECT Id = 8, Name = 'Product Listing Message') temp
ON temp.Id = hba.Id
WHEN NOT matched THEN
INSERT (Id, Name) VALUES (temp.Id, temp.Name);
您可以在关注之前检查此项，下面是示例
IF OBJECT_ID ('dbo.TargetTable') IS NOT NULL
DROP TABLE dbo.TargetTable
GO
CREATE TABLE dbo.TargetTable
(
Id INT NOT NULL,
Name VARCHAR (255) NOT NULL,
CONSTRAINT PK_TargetTable PRIMARY KEY (Id)
)
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('Unknown')
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('Mapping')
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('Update')
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('Message')
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('Switch')
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('Unmatched')
GO
INSERT INTO dbo.TargetTable (Name)
VALUES ('ProductMessage')
GO
Merge MyTargetTable hba
USING (SELECT Id = 8, Name = 'Listing Message') temp
ON temp.Id = hba.Id
WHEN NOT matched THEN
INSERT (Id, Name) VALUES (temp.Id, temp.Name);
答案 3 :(得分：2)
更多关于建议进一步阅读的评论链接...一篇非常好的博客文章，以各种方式完成此任务的基准can be found here。
他们使用了一些技巧：“插入不存在的位置”，“合并”语句，“插入除外”和典型的“左连接”，以查看哪种方式最快完成此任务。
每种技术使用的示例代码如下（从其页面直接复制/粘贴）：
INSERT INTO #table1 (Id, guidd, TimeAdded, ExtraData)
SELECT Id, guidd, TimeAdded, ExtraData
FROM #table2
WHERE NOT EXISTS (Select Id, guidd From #table1 WHERE #table1.id = #table2.id)
-----------------------------------
MERGE #table1 as [Target]
USING (select Id, guidd, TimeAdded, ExtraData from #table2) as [Source]
(id, guidd, TimeAdded, ExtraData)
on [Target].id =[Source].id
WHEN NOT MATCHED THEN
INSERT (id, guidd, TimeAdded, ExtraData)
VALUES ([Source].id, [Source].guidd, [Source].TimeAdded, [Source].ExtraData);
------------------------------
INSERT INTO #table1 (id, guidd, TimeAdded, ExtraData)
SELECT id, guidd, TimeAdded, ExtraData from #table2
EXCEPT
SELECT id, guidd, TimeAdded, ExtraData from #table1
------------------------------
INSERT INTO #table1 (id, guidd, TimeAdded, ExtraData)
SELECT #table2.id, #table2.guidd, #table2.TimeAdded, #table2.ExtraData
FROM #table2
LEFT JOIN #table1 on #table1.id = #table2.id
WHERE #table1.id is null
对于那些寻求速度的人来说，这是一个很好的阅读！在SQL 2014上，Insert-Except方法对于5000万或更多记录来说是最快的。
答案 4 :(得分：0)
隐藏重复的唯一约束不是一个解决方案吗？
INSERT IGNORE INTO tblSoftwareTitles...