Identity Sql Là Gì
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Trong bài viết này
Applies to:
Allows explicit values to be inserted into the identity column of a table.
Syntax
SET IDENTITY_INSERT < < database_name . > schema_name . > table_name { ON | OFF }
Note
To view Transact-SQL syntax for SQL Server 2014 and earlier, see Previous versions documentation.
Arguments
database_nameIs the name of the database in which the specified table resides.
schema_nameIs the name of the schema to which the table belongs.
table_nameIs the name of a table with an identity column.
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Remarks
At any time, only one table in a session can have the IDENTITY_INSERT property set to ON. If a table already has this property set to ON, and a SET IDENTITY_INSERT ON statement is issued for another table, SQL Server returns an error message that states SET IDENTITY_INSERT is already ON and reports the table it is set ON for.
If the value inserted is larger than the current identity value for the table, SQL Server automatically uses the new inserted value as the current identity value.
The setting of SET IDENTITY_INSERT is set at execute or run time and not at parse time.
Permissions
User must own the table or have ALTER permission on the table.
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Examples
The following example creates a table with an identity column and shows how the SET IDENTITY_INSERT setting can be used to fill a gap in the identity values caused by a DELETE statement.
USE AdventureWorks2012; GO -- Create tool table. CREATE TABLE dbo.Tool( ID INT IDENTITY NOT NULL PRIMARY KEY, Name VARCHAR(40) NOT NULL ); GO -- Inserting values into products table. INSERT INTO dbo.Tool(Name) VALUES ("Screwdriver") , ("Hammer") , ("Saw") , ("Shovel"); GO -- Create a gap in the identity values. DELETE dbo.Tool WHERE Name = "Saw"; GO SELECT * FROM dbo.Tool; GO -- Try to insert an explicit ID value of 3; -- should return an error:-- An explicit value for the identity column in table "AdventureWorks2012.dbo.Tool" can only be specified when a column list is used and IDENTITY_INSERT is ON.INSERT INTO dbo.Tool (ID, Name) VALUES (3, "Garden shovel"); GO -- SET IDENTITY_INSERT to ON. SET IDENTITY_INSERT dbo.Tool ON; GO -- Try to insert an explicit ID value of 3. INSERT INTO dbo.Tool (ID, Name) VALUES (3, "Garden shovel"); GO SELECT * FROM dbo.Tool; GO -- Drop products table. DROP TABLE dbo.Tool; GO
