Is there support for temporal tables in SQL Server?

Is there support for temporal tables in SQL Server?

SQL Server 2016 introduced support for temporal tables (also known as system-versioned temporal tables) as 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.

How is data modified in a temporal table?

Data in a system-versioned temporal table is modified using regular DML statements with one important difference: period column data cannot be directly modified. When data is updated, it is versioned, with the previous version of each updated row is inserted into the history table.

Are there any limitations to a temporal table?

There are also some limitations: Temporal and history table cannot be FILETABLE The history table cannot have any constraints INSERT and UPDATE statements cannot reference the SYSTEM_TIME period columns Data in the history table cannot be modified

How to delete rows from a temporal table?

Set SYSTEM_VERSIONING = OFF and delete rows from current and history table but keep in mind that way system will not preserve history of changes. TRUNCATE, SWITCH PARTITION OUT of current table and SWITCH PARTITION IN history table are not supported while SYSTEM_VERSIONING = ON.

Can a indexed view be used on a temporal table?

Indexed views are not supported on top of temporal queries (queries that use FOR SYSTEM_TIME clause). 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.

Which is the best indexing strategy for temporal data?

These are discussed later in this document in the section entitled Querying Temporal Data. An optimal indexing strategy will include a clustered columns store index and / or a B-tree rowstore index on the current table and a clustered columnstore index on the history table for optimal storage size and performance.

Can a temporal table be created from a history table?

During temporal table creation users can specify existing history table (must be schema compliant) or let system create default history table. Real data sources are dynamic and more often than not business decisions rely on insights that analysts can get from data evolution.

How to retrieve data from a temporal table?

Data retrieval is made very simple using the SYSTEM_TIME clause along with the associated sub-clause. The history table can grow big. It depends on the number of transactions on the temporal table so, space is the biggest tradeoff. You can consider purging the data from the history table.

What are the different types of temporal tables?

Following are the 3 types of tables. In this example we have a database called “TemporalDB”. It has a “Customer” table that has system_versioning = ON and the corresponding history table called “CustomerHistory”. There is also a non-temporal (normal) table called “CustomerDetail” in this database.

Why do we need metadata in SQL Server?

It also provides easy mechanism to query this historical data. There are quite a few Metadata (data about data) tables, views and functions that were added in the SQL Server engine to integrate and optimize this feature.

What do the columns in a temporal table do?

These columns are referred to as period columns. These period columns are used exclusively by the system to record period of validity for each row whenever a row is modified. In addition to these period columns, a temporal table also contains a reference to another table with a mirrored schema.

Do you need a primary key for a temporal table?

Consider the following when working with temporal tables: A temporal table must have a primary key defined in order to correlate records between the current table and the history table, and the history table cannot have a primary key defined.

How is the period of validity defined in a temporal table?

Within each of these tables, the following two additional datetime2 columns are used to define the period of validity for each row: Period start column: The system records the start time for the row in this column, typically denoted as the SysStartTime column.

How to query data in a system-versioned temporal tables in..?

This will return all current (actual) data: This will return all data changes ( Update, Delete, Merge) that were made in the dbo.People system versioned table: This clause will return all the rows from both the dbo.People system versioned and dbo.PeopleHistory history table.

What is the new for system _ time clause in SQL Server 2016?

The new FOR SYSTEM_TIME clause brings a lot of flexibility to SQL Server 2016 with regard to temporal tables. It has 4 different sub-clauses, each with a slightly different interpretation of how temporal data should be returned, allowing for powerful querying of system-versioned tables.

Do you need to know the name of the temporal table?

Note that it’s not necessary to know the name of the history table or how the temporal table is constructed. The use of the temporal table is transparent: you just query the table using the FOR SYSTEM_TIME clause and SQL Server handles all the rest.