Changing the schema of a system-versioned temporal table
Applies to: SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance
Use the ALTER TABLE statement to add, alter or remove a column.
Here are some examples that change the schema of temporal table.
ALTER TABLE dbo.Department ALTER COLUMN DeptName varchar(100); ALTER TABLE dbo.Department ADD WebAddress nvarchar(255) NOT NULL CONSTRAINT DF_WebAddress DEFAULT 'www.mycompany.com'; ALTER TABLE dbo.Department ADD TempColumn INT; GO ALTER TABLE dbo.Department DROP COLUMN TempColumn; /* Setting IsHidden property for period columns. Use ALTER COLUMN <period_column> DROP HIDDEN to clear IsHidden flag */ ALTER TABLE dbo.Department ALTER COLUMN SysStartTime ADD HIDDEN; ALTER TABLE dbo.Department ALTER COLUMN SysEndTime ADD HIDDEN;
CONTROL permission on current and history tables is required to change schema of temporal table.
During an ALTER TABLE operation, the system holds a schema lock on both tables.
Specified schema change is propagated to history table appropriately (depending on type of change).
If you add a non-nullable column or alter existing column to become non-nullable, you must specify the default value for existing rows. The system will generate an additional default with the same value and apply it to the history table. Adding DEFAULT to a non-empty table is a size of data operation on all editions other than SQL Server Enterprise Edition (on which it is a metadata operation).
Adding varchar(max), nvarchar(max), varbinary(max) or XML columns with defaults will be an update data operation on all editions of SQL Server.
If row size after column addition exceeds the row size limit, new columns cannot be added online.
Once you extend a table with a new NOT NULL column, consider dropping default constraint on the history table as all columns in that table are automatically populated by the system.
Online option (WITH (ONLINE = ON) has no effect on ALTER TABLE ALTER COLUMN in case of system-versioned temporal table. ALTER column is not performed as online regardless of which value was specified for ONLINE option.
You can use ALTER COLUMN to change IsHidden property for period columns.
You cannot use direct ALTER for the following schema changes. For these types of changes, set SYSTEM_VERSIONING = OFF.
- Adding a computed column
- Adding an IDENTITY column
- Adding a SPARSE column or changing existing column to be SPARSEwhen the history table is set to DATA_COMPRESSION = PAGE or DATA_COMPRESSION = ROW, which is the default for the history table.
- Adding a COLUMN_SET
- Adding a ROWGUIDCOL column or changing existing column to be ROWGUIDCOL
The following example demonstrates changing the schema where setting SYSTEM_VERSIONING = OFF is still required (adding IDENTITY column). This example disables the data consistency check. This check is unnecessary when the schema change is made within a transaction as no concurrent data changes can occur.
BEGIN TRAN ALTER TABLE [dbo].[CompanyLocation] SET (SYSTEM_VERSIONING = OFF); ALTER TABLE [CompanyLocation] ADD Cntr INT IDENTITY (1,1); ALTER TABLE [dbo].[CompanyLocationHistory] ADD Cntr INT NOT NULL DEFAULT 0; ALTER TABLE [dbo].[CompanyLocation] SET ( SYSTEM_VERSIONING = ON ( HISTORY_TABLE = [dbo].[CompanyLocationHistory]) ); COMMIT ;
- Temporal Tables Getting Started with System-Versioned Temporal Tables
- Manage Retention of Historical Data in System-Versioned Temporal Tables
- System-Versioned Temporal Tables with Memory-Optimized Tables
- ALTER TABLE (Transact-SQL)
- Creating a System-Versioned Temporal Table
- Modifying Data in a System-Versioned Temporal Table
- Querying Data in a System-Versioned Temporal Table
- Stopping System-Versioning on a System-Versioned Temporal Table