最佳答案Identity_Insert in SQL ServerIntroduction: Identity_Insert is a feature in SQL Server that allows explicit insertion of values into an identity column. Normally...
Identity_Insert in SQL Server
Introduction:
Identity_Insert is a feature in SQL Server that allows explicit insertion of values into an identity column. Normally, when a table has an identity column, the system automatically generates a unique value for each new row inserted into the table. However, there are situations where we may need to insert specific values into the identity column instead of the system-generated ones. Identity_Insert provides a way to temporarily disable this automatic generation and allows us to manually insert values into the identity column.
Usage:
To use Identity_Insert, we need to first enable it for the table we are working with. This can be done using the SET IDENTITY_INSERT statement in SQL Server Management Studio:
SET IDENTITY_INSERT TableName ON;After enabling Identity_Insert for the table, we can now explicitly insert values into the identity column:
INSERT INTO TableName (IdentityColumn, OtherColumns) VALUES (Value1, Value2);Once we have finished inserting the desired values, we can disable Identity_Insert using the same SET IDENTITY_INSERT statement:
SET IDENTITY_INSERT TableName OFF;Use Cases:
1. Migrating Data:
Identity_Insert is commonly used when migrating data from one table to another, particularly when the identity column values need to remain the same in the destination table. By enabling Identity_Insert, we can efficiently transfer the data, including the identity values, without any disruptions.
2. Importing Specific Records:
There are scenarios when we may want to import specific records from one table to another. In such cases, Identity_Insert allows us to insert the selected records into the destination table along with their original identity values.
3. Seed Starting Value:
Sometimes, due to certain requirements or business rules, we may need to change the starting value of an identity column. However, altering the identity seed value is not possible directly. In this situation, we can create a new table with Identity_Insert enabled, insert the desired starting value into the identity column, and then move the data from the old table to the new one. This technique can be useful when we want to consolidate data or restructure a table.
Important Considerations:
When using Identity_Insert, there are a few important considerations to keep in mind:
1. Permissions:
Enabling or disabling Identity_Insert requires appropriate permissions. By default, only members of the sysadmin or db_owner roles have the necessary rights. Other users need explicit permission granted by a system administrator or a user with administrative rights on the database.
2. Single Table at a Time:
Identity_Insert is applicable on a per-table basis. It means we can enable Identity_Insert for one table while keeping it disabled for others simultaneously. This allows for granular control over specific tables during data manipulation operations.
3. Only for Identity Columns:
Identity_Insert can only be used when inserting values into the identity column of a table. It does not apply to other non-identity columns in the table.
Conclusion:
Identity_Insert is a useful feature in SQL Server that allows explicit insertion of values into an identity column. It can be handy in various scenarios such as data migration, importing specific records, or changing the starting value of an identity column. However, it is important to exercise caution while using this feature and ensure that appropriate permissions are granted. Understanding and utilizing Identity_Insert effectively can greatly enhance our ability to handle data manipulation tasks in SQL Server.
