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DBCC CHECKIDENT (Transact-SQL)

  • Članak

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics

Checks the current identity value for the specified table in SQL Server and, if needed, changes the identity value. You can also use DBCC CHECKIDENT to manually set a new current identity value for the identity column.

Transact-SQL syntax conventions

Syntax

Syntax for SQL Server and Azure SQL Database:

DBCC CHECKIDENT
 (
    table_name
        [ , { NORESEED | { RESEED [ , new_reseed_value ] } } ]
)
[ WITH NO_INFOMSGS ]

Syntax for Azure Synapse Analytics:

DBCC CHECKIDENT
 (
    table_name
        [ RESEED , new_reseed_value ]
)
[ WITH NO_INFOMSGS ]

Arguments

table_name

The name of the table for which to check the current identity value. The table specified must contain an identity column. Table names must follow the rules for identifiers. Two or three part names must be delimited, such as Person.AddressType or [Person].[AddressType].

NORESEED

Specifies that the current identity value shouldn't be changed.

RESEED

Specifies that the current identity value should be changed.

new_reseed_value

The new value to use as the current value of the identity column.

WITH NO_INFOMSGS

Suppresses all informational messages.

Remarks

The specific corrections made to the current identity value depend on the parameter specifications.

DBCC CHECKIDENT command Identity correction or corrections made
DBCC CHECKIDENT (<table_name>, NORESEED) Current identity value isn't reset. DBCC CHECKIDENT returns the current identity value and the current maximum value of the identity column. If the two values aren't the same, you should reset the identity value to avoid potential errors or gaps in the sequence of values.
DBCC CHECKIDENT (<table_name>)

or

DBCC CHECKIDENT (<table_name>, RESEED)		 If the current identity value for a table is less than the maximum identity value stored in the identity column, it is reset using the maximum value in the identity column. See the Exceptions section that follows.
DBCC CHECKIDENT (<table_name>, RESEED, <new_reseed_value>) Current identity value is set to the new_reseed_value. If no rows have been inserted into the table since the table was created, or if all rows have been removed by using the TRUNCATE TABLE statement, the first row inserted after you run DBCC CHECKIDENT uses new_reseed_value as the identity. If rows are present in the table, or if all rows have been removed by using the DELETE statement, the next row inserted uses new_reseed_value + the current increment value. If a transaction inserts a row and is later rolled back, the next row inserted uses new_reseed_value + the current increment value as if the row had been deleted. If the table isn't empty, setting the identity value to a number less than the maximum value in the identity column can result in one of the following conditions:

- If a PRIMARY KEY or UNIQUE constraint exists on the identity column, error message 2627 will be generated on later insert operations into the table because the generated identity value will conflict with existing values.

- If a PRIMARY KEY or UNIQUE constraint doesn't exist, later insert operations will result in duplicate identity values.

Exceptions

The following table lists conditions when DBCC CHECKIDENT doesn't automatically reset the current identity value, and provides methods for resetting the value.

Condition Reset methods
The current identity value is larger than the maximum value in the table. Execute DBCC CHECKIDENT (<table_name>, NORESEED) to determine the current maximum value in the column. Next, specify that value as the new_reseed_value in a DBCC CHECKIDENT (<table_name>, RESEED, <new_reseed_value>) command.

or

Execute DBCC CHECKIDENT (<table_name>, RESEED,<new_reseed_value>) with new_reseed_value set to a low value, and then run DBCC CHECKIDENT (<table_name>, RESEED) to correct the value.
All rows are deleted from the table. Execute DBCC CHECKIDENT (<table_name>, RESEED, <new_reseed_value>) with new_reseed_value set to the new starting value.

Change the seed value

The seed value is the value inserted into an identity column for the first row loaded into the table. All subsequent rows contain the current identity value plus the increment value where current identity value is the last identity value generated for the table or view.

You can't use DBCC CHECKIDENT for the following tasks:

  • Change the original seed value specified for an identity column when the table or view was created.

  • Reseed existing rows in a table or view.

To change the original seed value and reseed any existing rows, drop the identity column and recreate it specifying the new seed value. When the table contains data, the identity numbers are added to the existing rows with the specified seed and increment values. The order in which the rows are updated isn't guaranteed.

Result sets

Whether or not you specify any options for a table that contains an identity column, DBCC CHECKIDENT returns the following message for all operations except one. That operation is specifying a new seed value.

Checking identity information: current identity value '<current identity value>', current column value '<current column value>'. DBCC execution completed. If DBCC printed error messages, contact your system administrator.

When DBCC CHECKIDENT is used to specify a new seed value by using RESEED <new_reseed_value>, the following message is returned.

Checking identity information: current identity value '<current identity value>'. DBCC execution completed. If DBCC printed error messages, contact your system administrator.

Permissions

Caller must own the schema that contains the table, or be a member of the sysadmin fixed server role, the db_owner fixed database role, or the db_ddladmin fixed database role.

Azure Synapse Analytics requires db_owner permissions.

Examples

A. Reset the current identity value, if it's needed

The following example resets the current identity value, if it's needed, of the specified table in the AdventureWorks2022 database.

USE AdventureWorks2022;
GO
DBCC CHECKIDENT ('Person.AddressType');
GO

B. Report the current identity value

The following example reports the current identity value in the specified table in the AdventureWorks2022 database, and doesn't correct the identity value if it's incorrect.

USE AdventureWorks2022;
GO
DBCC CHECKIDENT ('Person.AddressType', NORESEED);
GO

C. Force the current identity value to a new value

The following example forces the current identity value in the AddressTypeID column in the AddressType table to a value of 10. Because the table has existing rows, the next row inserted will use 11 as the value. The new current identity value defined for the column plus 1 (which is the column's increment value).

USE AdventureWorks2022;
GO
DBCC CHECKIDENT ('Person.AddressType', RESEED, 10);
GO

D. Reset the identity value on an empty table

The following example assumes a table identity of (1, 1) and forces the current identity value in the ErrorLogID column in the ErrorLog table to a value of 1, after deleting all records from table. Because the table has no existing rows, the next row inserted will use 1 as the value, that is, the new current identity value without adding the increment value defined for the column after TRUNCATE, or adding the increment value after DELETE.

USE AdventureWorks2022;
GO
TRUNCATE TABLE dbo.ErrorLog
GO
DBCC CHECKIDENT ('dbo.ErrorLog', RESEED, 1);
GO
DELETE FROM dbo.ErrorLog
GO
DBCC CHECKIDENT ('dbo.ErrorLog', RESEED, 0);
GO

See also