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The times recorded in the system datetime2 columns are based on the begin time of the transaction itself. MERGE: The operation behaves exactly as if up to three statements (an INSERT, an UPDATE, and/or a DELETE) executed, depending on what is specified as actions in the MERGE statement.Only queries that deal with history data return data for which a row is closed. Queries of the current table won't return this row. In the current table, the row is removed. This marks the row as closed, with a period recorded for which the previous row was valid. DELETES: The system stores the previous value of the row in the history table and sets the value for the ValidTo column to the begin time of the current transaction (in the UTC time zone) based on the system clock.The value for the updated row in the current table for the ValidTo column remains the maximum value of. In the current table, the row is updated with its new value and the system sets the value for the ValidFrom column to the begin time for the transaction (in the UTC time zone) based on the system clock. This marks the row as closed, with a period recorded for which the row was valid. UPDATES: The system stores the previous value of the row in the history table and sets the value for the ValidTo column to the begin time of the current transaction (in the UTC time zone) based on the system clock.INSERTS: The system sets the value for the ValidFrom column to the begin time of the current transaction (in the UTC time zone) based on the system clock and assigns the value for the ValidTo column to the maximum value of.WITH (SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.EmployeeHistory)) įor more information, see Creating a System-Versioned Temporal Table. , PERIOD FOR SYSTEM_TIME (ValidFrom, ValidTo) , datetime2 GENERATED ALWAYS AS ROW START The following script illustrates a scenario with employee information: CREATE TABLE dbo.Employee The history table contains each previous value (the old version) for each row, if any, and the start time and end time for the period for which it was valid. The current table contains the current value for each row. Period end column: The system records the end time for the row in this column, typically denoted as the ValidTo column.Period start column: The system records the start time for the row in this column, typically denoted as the ValidFrom column.Within each of these tables, two additional datetime2 columns are used to define the period of validity for each row: System-versioning for a table is implemented as a pair of tables, a current table and a history table. Recovering from accidental data changes and application errors.Maintaining a slowly changing dimension for decision support applications.Reconstructing state of the data as of any time in the past.Auditing all data changes and performing data forensics when necessary.Real data sources are dynamic and more often than not business decisions rely on insights that analysts can get from data evolution. During temporal table creation users can specify an existing history table (which must be schema compliant) or let the system create a default history table.

The system uses the history table to automatically store the previous version of the row each time a row in the temporal table gets updated or deleted. In addition to these period columns, a temporal table also contains a reference to another table with a mirrored schema, called the history table.

The main table that stores current data is referred to as the current table, or simply as the temporal table. These period columns are used exclusively by the system to record the period of validity for each row, whenever a row is modified. These columns are referred to as period columns. This type of temporal table is referred to as a system-versioned temporal table because the period of validity for each row is managed by the system (that is, the database engine).Įvery temporal table has two explicitly defined columns, each with a datetime2 data type.

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What is a system-versioned temporal table?Ī system-versioned temporal table is a type of user table designed to keep a full history of data changes, allowing easy point-in-time analysis. You can Get Started with System-Versioned Temporal Tables, and review Temporal Table Usage Scenarios. Temporal tables (also known as system-versioned temporal tables) are a database feature that brings built-in support for providing information about data stored in the table at any point in time, rather than only the data that is correct at the current moment in time.

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