Temporal Tables in SQL Server 2016

Temporal, or system-versioned tables which was introduced in SQL Server 2016, allow us to go back in time and see what the data in table looked like at that point in time. We can say a system-versioned temporal table is a type of user table designed to keep a full history of data changes and allow easy point in time analysis. 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.

What are the usage of Temporal Tables ?

The most common business uses for temporal tables are:

1. Slowly changing dimensions. The temporal tables provide a simpler way to querying data that is current for a specified period of time, such as time slicing data, that well-known problem on Data Warehousing databases.
2. Data Auditing. The temporal tables provide an audit trail to determine when data was modified in the “parent” table.
3. Temporal tables allow you to query data as it was at a particular point in time to examine the state of the data as it was then.
4. Analyzing trends by understanding how the data changes over time with the ongoing business activity, and to calculate trends in the way that data changes over time.
5. Repairing or recovering record level corruptions.

How does Temporal Tables works ?

1. When we create temporal table, it uses two tables – one for live data, the other for historical versions – to store current and prior row versions. 
2. Temporal tables are created on a table-by-table basis, which means can choose only the tables you want to include in this versioning architecture without impacting conventional (non-versioned) tables.
3. When designing a table that will be used as a temporal table, three things are required: 

• A primary key.
• A non-nullable DATETIME2 column to store the starting effective date.
• A non-nullable DATETIME2 column to store the ending effective date.
• When creating the temporal table, it is recommended to create the effective date columns as hidden. 

What are the limitations of Temporal tables ?

There are some requirements and limitations of temporal tables as below :

• Every table should have a Primary Key is required .
• A History table must be created in the same database as the current table.
• Linked servers are not supported.
• INSERT and UPDATE statements cannot reference SYSTEM_TIME period columns.
• The Truncate table operation is not supported on temporal tables.
• A System-Versioned table does not allowed any constraints.
• We can’t modify the data in history table.

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