DBCC CHECKIDENT (Transact-SQL)
Checks the current identity value for the specified table in SQL Server 2012 and, if it is needed, changes the identity value. You can also use DBCC CHECKIDENT to manually set a new current identity value for the identity column.
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Transact-SQL Syntax Conventions
Składnia
DBCC CHECKIDENT
(
table_name
[, { NORESEED | { RESEED [, new_reseed_value ] } } ]
)
[ WITH NO_INFOMSGS ]
Arguments
table_name
Is the name of the table for which to check the current identity value. The table specified must contain an identity column. Table names must comply with the rules for identifiers.NORESEED
Specifies that the current identity value should not be changed.RESEED
Specifies that the current identity value should be changed.new_reseed_value
Is the new value to use as the current value of the identity column.WITH NO_INFOMSGS
Suppresses all informational messages.
Uwagi
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 is not reset. DBCC CHECKIDENT returns the current identity value and the current maximum value of the identity column. If the two values are not 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. Otherwise, the next row inserted uses new_reseed_value + the current increment value. If the table is not 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:
|
Exceptions
The following table lists conditions when DBCC CHECKIDENT does not 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. |
or
|
All rows are deleted from the table. |
Execute DBCC CHECKIDENT (table_name, RESEED, new_reseed_value) with new_reseed_value set to the desired starting value. |
Changing the Seed Value
The seed value is the value inserted into an identity column for the very 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 cannot use DBCC CHECKIDENT to perform the following tasks:
Change the original seed value that was 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, you must 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 is not guaranteed.
Result Sets
Whether or not any of the options are specified for a table that contains an identity column, DBCC CHECKIDENT returns the following message for all operations except when 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 table, or be a member of the sysadmin fixed server role, the db_owner fixed database role, or the db_ddladmin fixed database role.
Examples
A. Resetting the current identity value, if it is needed
The following example resets the current identity value, if it is needed, of the specified table in the AdventureWorks2012 database.
USE AdventureWorks2012;
GO
DBCC CHECKIDENT ('Person.AddressType');
GO
B. Reporting the current identity value
The following example reports the current identity value in the specified table in the AdventureWorks2012 database, and does not correct the identity value if it is incorrect.
USE AdventureWorks2012;
GO
DBCC CHECKIDENT ('Person.AddressType', NORESEED);
GO
C. Forcing 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, that is, the new current increment value defined for the column value plus 1.
USE AdventureWorks2012;
GO
DBCC CHECKIDENT ('Person.AddressType', RESEED, 10);
GO
Zobacz także
Odwołanie
IDENTITY (Property) (Transact-SQL)