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问题:
OK so I'm trying to improve my asp data entry page to ensure that the entry going into my data table is unique.
So in this table I have SoftwareName and SoftwareType. I'm trying to get it so if the entry page sends an insert query with parameters that match whats in the table (so same title and type) then an error is thrown up and the Data isn't entered.
Something like this:
INSERT INTO tblSoftwareTitles( SoftwareName, SoftwareSystemType) VALUES(@SoftwareName,@SoftwareType) WHERE NOT EXISTS (SELECT SoftwareName FROM tblSoftwareTitles WHERE Softwarename = @SoftwareName AND SoftwareType = @Softwaretype)
So This syntax works great for Selecting columns from one table into another without duplicates being entered but doesn't seem to want to work with a parametrized insert query. can anyone help me out with this?
Cheers Dan
Edit:
Here's the code I'm using in my asp insert method
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); } } }
回答1:
I would do this using and IF statement:
IF NOT EXISTS ( SELECT 1 FROM tblSoftwareTitles WHERE Softwarename = @SoftwareName AND SoftwareSystemType = @Softwaretype ) BEGIN INSERT tblSoftwareTitles (SoftwareName, SoftwareSystemType) VALUES (@SoftwareName, @SoftwareType) END;
You could do it without IF using SELECT
INSERT tblSoftwareTitles (SoftwareName, SoftwareSystemType) SELECT @SoftwareName,@SoftwareType WHERE NOT EXISTS ( SELECT 1 FROM tblSoftwareTitles WHERE Softwarename = @SoftwareName AND SoftwareSystemType = @Softwaretype );
Both methods are susceptible to a race condition, so while I would still use one of the above to insert, but you can safeguard duplicate inserts with a unique constraint:
CREATE UNIQUE NONCLUSTERED INDEX UQ_tblSoftwareTitles_Softwarename_SoftwareSystemType ON tblSoftwareTitles (SoftwareName, SoftwareSystemType);
Example on SQL-Fiddle
ADDENDUM
In SQL Server 2008 or later you can use MERGE with HOLDLOCK to remove the chance of a race condition (which is still not a substitute for a unique constraint).
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);
Example of Merge on SQL Fiddle
回答2:
This isn't an answer. I just want to show that IF NOT EXISTS(...) INSERT method isn't safe. You have to execute first Session #1 and then Session #2. After v #2 you will see that without an UNIQUE index you could get duplicate pairs (SoftwareName,SoftwareSystemType). Delay from session #1 is used to give you enough time to execute the second script (session #2). You could reduce this delay.
Session #1 (SSMS > New Query > F5 (Execute))
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;
Session #2 (SSMS > New Query > F5 (Execute))
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;
Results:
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
回答3:
There is a great solution for this problem ,You can use the Merge Keyword of Sql
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);
You can check this before following, below is the sample
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);
回答4:
More of a comment link for suggested further reading...A really good blog article which benchmarks various ways of accomplishing this task can be found here.
They use a few techniques: "Insert Where Not Exists", "Merge" statement, "Insert Except", and your typical "left join" to see which way is the fastest to accomplish this task.
The example code used for each technique is as follows (straight copy/paste from their page) :
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
It's a good read for those who are looking for speed! On SQL 2014, the Insert-Except method turned out to be the fastest for 50 million or more records.
回答5:
Ingnoring the duplicated unique constraint isn't a solution?
INSERT IGNORE INTO tblSoftwareTitles...
