Tag Archives: Temporal Table

Temporal Tables in Sql Server 2016 Part 4: DDL operations on the System-Versioned Temporal Table

Sql Server, Sql Server 2016, , , , , , , , , , , , ,

This is the fourth article in the series of articles on the Temporal Tables, below is the complete list of articles on System-Versioned Temporal Tables. This article will cover DDL operations on the System-Versioned Temporal Table with extensive list of examples

Let us create a Temporal Table by using the following script:

 
--Create demo database if it is not present
IF DB_ID('SqlhintsTemporalDemoDB') IS NULL
BEGIN   
    CREATE DATABASE SqlhintsTemporalDemoDB
END
GO
USE SqlhintsTemporalDemoDB
GO
--Create System-Versioned Temporal Table
CREATE TABLE dbo.Customer 
(  
  Id INT NOT NULL PRIMARY KEY CLUSTERED,
  Name NVARCHAR(100) NOT NULL, 
  StartTime DATETIME2 GENERATED ALWAYS AS ROW START
            HIDDEN NOT NULL,
  EndTime   DATETIME2 GENERATED ALWAYS AS ROW END 
            HIDDEN NOT NULL,
  PERIOD FOR SYSTEM_TIME (StartTime, EndTime)   
) 
WITH(SYSTEM_VERSIONING= ON (HISTORY_TABLE=dbo.CustomerHistory))

The above script will create the Temporal Table dbo.Customer and the corresponding History Table dbo.CustomerHistory as shown in the following image

SSMS View of Temporal and History Table

Let us try to add a column City to the temporal table by executing the following script

ALTER TABLE dbo.Customer ADD City NVARCHAR(50)

Post executing the above statement, check the columns in the Temporal and History table

Adding a column to the Temporal Table

We can see that adding a column to the Temporal Table adds the column to the History Table too

Let us try to drop the newly added column by the following script

ALTER TABLE dbo.Customer DROP COLUMN City

Post executing the above statement, check the columns in the Temporal and History table

Dropping a column from a Temporal Table

We can see that dropping a column from the Temporal Table drops the column from the history table too

Let us try to add a column directly to the History table by executing the following script

ALTER TABLE dbo.CustomerHistory ADD Country NVARCHAR(50)

RESULT

Msg 13550, Level 16, State 1, Line 1
Add column operation failed on table ‘SqlhintsTemporalDemoDB.dbo.CustomerHistory’ because it is not supported operation on system-versioned temporal tables.

From the above result we can see that when SYSTEM-VERSIONING is ON we can’t perform DDL operations on the HISTORY table but we can add indexes and default constraint on the History table.

History table can’t have constraints like : Primary key, foreign key, table or column constraints. Properties like Period definition, Identity definition, Indexes, Statistics, Check Constraints, Triggers, Permission, Partitioning Configuration is not replicated from the temporal/current table to the history table when it is created.

Below image shows that the primary key is not replicated from the Temporal Table to History Table when it is created.

Primar Key is not propogated to the history table

One more important point to note that the history table by default is page compressed

Dropping a Temporal Table

Let us try to drop a Temporal Table by executing the below statement

DROP TABLE dbo.Customer

RESULT

Msg 13552, Level 16, State 1, Line 1
Drop table operation failed on table ‘SqlhintsTemporalDemoDB.dbo.Customer’ because it is not supported operation on system-versioned temporal tables.

From the above result we can see that when SYSTEM-VERSIONING is ON we can’t drop a Temporal table

Disabling System Versioning

We can disable system versioning by executing the following statement:

ALTER TABLE dbo.Customer SET (SYSTEM_VERSIONING = OFF)

After executing the above statement the System Versioning is disabled and Temporal and History table will become like any other regular table as shown in the following image:

Disabling System Versioning

Now try to update the Period columns in the dbo.Customer table

UPDATE dbo.Customer
SET 	StartTime = GETUTCDATE()
WHERE Id = 1

RESULT

Msg 13537, Level 16, State 1, Line 19
Cannot update GENERATED ALWAYS columns in table ‘SqlhintsTemporalDemoDB.dbo.Customer’.

From the above result it is clear that even after disabling the SYSTEM_VERSIONING, we will not be able to update the PERIOD column values. To allow the PERIOD column value update we have to drop the PERIOD definition by executing the following statement

ALTER TABLE dbo.Customer
DROP PERIOD FOR SYSTEM_TIME

Now once again try updating by executing the following script

UPDATE dbo.Customer
SET 	StartTime = GETUTCDATE()
WHERE Id = 1

RESULT
Updating Temporal Table PERIOD column value

Now try to drop the dbo.Customer and dbo.CustomerHistory tables by executing the following script:

DROP TABLE dbo.Customer
GO
DROP TABLE dbo.CustomerHistory

RESULT
Dropping Regular Tables

In Summary below is the script to drop System-Versioned Temporal Tables

--First disable the system versioning
ALTER TABLE dbo.Employee
    SET (SYSTEM_VERSIONING = OFF)
GO
--Drop Period definition.
--This will allow manipulations on the PERIOD columns
ALTER TABLE dbo.Employee
DROP PERIOD FOR SYSTEM_TIME
GO
--Now drop Employee and EmployeeHistory tables
--(To drop these tables, dropping PERIOD definition is optional)
DROP TABLE dbo.Customer
DROP TABLE dbo.CustomerHistory

Temporal Tables in Sql Server 2016 Part 3: Enabling System Versioning for an Existing Regular Table

Sql Server, Sql Server 2016, , , , , , , , , , , , , , , , , , ,

This is the third article in the series of articles on the Temporal Tables, below is the complete list of articles on System-Versioned Temporal Tables. This article explains how we can enable system versioning on an existing regular table and link it to a new or existing table as history table.

Let us first create demo database by using the following script

IF DB_ID('SqlhintsTemporalDemoDB') IS NULL
BEGIN
    CREATE DATABASE SqlhintsTemporalDemoDB
END
GO
USE SqlhintsTemporalDemoDB
GO

Enabling System-Versioning for an existing regular table and linking it to a new history table

Let us first create a regular Product table with Sample data by executing the following script:

CREATE TABLE dbo.product
(  
  Id INT NOT NULL PRIMARY KEY CLUSTERED,
  Name NVARCHAR(100) NOT NULL
)
GO
INSERT INTO dbo.Product VALUES( 1, 'Television')
GO

Now try to enable the system versioning by executing the below statement:

ALTER TABLE dbo.Product
SET (SYSTEM_VERSIONING = ON)

RESULT

Msg 13510, Level 16, State 1, Line 1
Cannot set SYSTEM_VERSIONING to ON when SYSTEM_TIME period is not defined.

From the result it is clear that to enable system-versioning the table needs to have two period DATETIME2 columns with period definition in it.

Let’s try to add the two datetime2 datatype period columns and the period definition by the following script

ALTER TABLE dbo.Product
ADD StartTime DATETIME2 GENERATED ALWAYS AS ROW START
              HIDDEN  NULL,
   EndTime DATETIME2 GENERATED ALWAYS AS ROW END
              HIDDEN  NULL,
   PERIOD FOR SYSTEM_TIME (StartTime, EndTime)

RESULT

Msg 13587, Level 16, State 1, Line 1
Period column ‘StartTime’ in a system-versioned temporal table cannot be nullable.

From the result it is clear that the period columns shouldn’t be nullable column.

Now try to execute the below statement to add two datetime2 type NOT NULL period columns (if null constraint is not specified for period columns they are considered as NOT NULL) and the period definition:

  
ALTER TABLE dbo.Product
ADD StartTime DATETIME2 GENERATED ALWAYS AS ROW START HIDDEN,
   EndTime   DATETIME2 GENERATED ALWAYS AS ROW END HIDDEN,
   PERIOD FOR SYSTEM_TIME (StartTime, EndTime)

RESULT

Msg 4901, Level 16, State 1, Line 1
ALTER TABLE only allows columns to be added that can contain nulls, or have a DEFAULT definition specified, or the column being added is an identity or timestamp column, or alternatively if none of the previous conditions are satisfied the table must be empty to allow addition of this column. Column ‘StartTime’ cannot be added to non-empty table ‘Product’ because it does not satisfy these conditions.

From the result it is clear that we are not allowed to add NOT NULL columns to an existing table with data in it.

Let us now try to add NOT NULL PERIOD columns to the existing table with DEFAULT value by executing the following statement:

ALTER TABLE dbo.Product
ADD StartTime DATETIME2 GENERATED ALWAYS AS ROW START
  HIDDEN DEFAULT GETUTCDATE(),
 EndTime  DATETIME2 GENERATED ALWAYS AS ROW END
  HIDDEN DEFAULT 
     CONVERT(DATETIME2, '9999-12-31 23:59:59.9999999'),
 PERIOD FOR SYSTEM_TIME (StartTime, EndTime)

We have successfully added the PERIOD columns and PERIOD definition to the Product table, now enable the system versioning by executing the below statement. Here we are mentioning the new history table name as dbo.ProductHistoy. Specifying History table name is optional, if we don’t specify the history table name then Sql Server creates a new history table with name like MSSQL_TemporalHistoryFor

ALTER TABLE dbo.Product
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory))
GO

After executing the above statement, if we look into the SSMS window we can see that a dbo.Product table is marked as System-Versioned table. Inside this table we can see a new nested table dbo.ProductHistory table created and marked as History Table as shown below.

SSMS View of Temporal Table Product 1

SUMMARY

Below is the script for enabling System-Versioning for an existing regular table and linking it to a new history table

BEGIN TRAN
--Add two PERIOD datetime2 columns and PERIOD definition 
ALTER TABLE dbo.Product
ADD StartTime DATETIME2 GENERATED ALWAYS AS ROW START
   HIDDEN NOT NULL DEFAULT GETUTCDATE(),
 EndTime   DATETIME2 GENERATED ALWAYS AS ROW END
   HIDDEN  NOT NULL DEFAULT 
     CONVERT(DATETIME2, '9999-12-31 23:59:59.9999999'),
 PERIOD FOR SYSTEM_TIME (StartTime, EndTime)
--Enable System Versioning
ALTER TABLE dbo.Product
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory))
COMMIT TRAN

CLEAN-UP

Let us drop the Product and ProductHistory tables by the following script

--Disable the system versioning
ALTER TABLE dbo.Product
    SET (SYSTEM_VERSIONING = OFF)
GO
--Drop Period definition
ALTER TABLE dbo.Product
DROP PERIOD FOR SYSTEM_TIME
GO
--Now drop Product and ProductHistory tables
DROP TABLE dbo.Product
DROP TABLE dbo.ProductHistory

Enabling System-Versioning for an existing regular table and linking it to an existing history table

Let us create a regular Product and ProductHistory table by using the following script:

---Create a regular Product table
CREATE TABLE [dbo].[Product](
	[ProductId] [int] NOT NULL PRIMARY KEY CLUSTERED ,
	[Name] [nvarchar](100) NOT NULL,	
	[StartTime] DATETIME NOT NULL,
	[EndTime] DATETIME NOT NULL,
	[Price] [float] NULL
) 
GO
---Create a regular ProductHistory table
CREATE TABLE [dbo].[ProductHistory](
	[ProductHistoryId] [int] IDENTITY(1,1) NOT NULL ,
	[ProductId] [int] NOT NULL,
	[Name] [nvarchar](100) NOT NULL,
	[StartTime] DATETIME NOT NULL,
	[EndTime] DATETIME NOT NULL,
	CONSTRAINT [PK_ProductHistory] 
             PRIMARY KEY  CLUSTERED ([ProductHistoryId]), 
	CONSTRAINT FK_ProductHistory_Product 
             FOREIGN KEY ([ProductId])
	REFERENCES Product([ProductId])
) ON [PRIMARY]
GO

Let us execute the following statement to enable System-Versioning for the Product table and link it to an existing table ProductHistory as the history table

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )
GO

RESULT

Msg 13510, Level 16, State 1, Line 23
Cannot set SYSTEM_VERSIONING to ON when SYSTEM_TIME period is not defined.

From the result it is clear that to enable system-versioning table needs to have PERIOD definition

Let us try to add PERIOD definition to the table by using the following script

ALTER TABLE dbo.Product
ADD PERIOD FOR SYSTEM_TIME (StartTime, EndTime)

RESULT

Msg 13501, Level 16, State 3, Line 31
Temporal generated always column ‘StartTime’ has invalid data type.

From the result it is clear that PERIOD column has invalid data type

Let us change the data type of the PERIOD columns to DATETIME2 type and then add the PERIOD definition

--Alter StartTime Column type to DATETIME2
ALTER TABLE dbo.Product
ALTER COLUMN  [StartTime] DATETIME2 NOT NULL
--Alter EndTime Column type to DATETIME2
ALTER TABLE dbo.Product
ALTER COLUMN  [EndTime] DATETIME2 NOT NULL
GO
--Add the period definition
ALTER TABLE dbo.Product
ADD PERIOD FOR SYSTEM_TIME (StartTime, EndTime)

Now try to enable System-Versioning

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )

RESULT

Msg 13515, Level 16, State 1, Line 55
Setting SYSTEM_VERSIONING to ON failed because history table ‘SqlhintsTemporalDemoDB.dbo.ProductHistory’ has custom unique keys defined. Consider dropping all unique keys and trying again.

From the error it is clear that System-Versioning can’t be enabled when we primary key on the history table.

Let us drop the primary key from ProductHistoryId column by the following script

ALTER TABLE ProductHistory
DROP CONSTRAINT [PK_ProductHistory]

Now try to enable System-Versioning

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )

RESULT

Msg 13516, Level 16, State 1, Line 67
Setting SYSTEM_VERSIONING to ON failed because history table ‘SqlhintsTemporalDemoDB.dbo.ProductHistory’ has foreign keys defined. Consider dropping all foreign keys and trying again.

From the above error it is clear that we can’t enable SYSTEM_VERSIONING when history table has foreign key constraints

Let us drop the foreign key constraint using the following script

ALTER TABLE ProductHistory
DROP CONSTRAINT FK_ProductHistory_Product

Now try to enable System-Versioning

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )

RESULT

Msg 13518, Level 16, State 1, Line 83
Setting SYSTEM_VERSIONING to ON failed because history table ‘SqlhintsTemporalDemoDB.dbo.ProductHistory’ has IDENTITY column specification. Consider dropping all IDENTITY column specifications and trying again.

From the error it is clear that we can’t enable system-versioning when the history table has identity columns in it

Let us drop the identity coluimn [ProductHistoryId] from the ProductHistory table using the following script

ALTER TABLE [dbo].[ProductHistory]
DROP COLUMN [ProductHistoryId]

Now try to enable System-Versioning

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )

RESULT

Msg 13523, Level 16, State 1, Line 99
Setting SYSTEM_VERSIONING to ON failed because table ‘SqlhintsTemporalDemoDB.dbo.Product’ has 5 columns and table ‘SqlhintsTemporalDemoDB.dbo.ProductHistory’ has 4 columns.

From the above error it is clear that to enable system versioning the number columns in the Temporal and the history tables should be same.

Let us add price column to the ProductHistory table too

ALTER TABLE [dbo].[ProductHistory]
ADD [Price] [Float]

Now try to enable System-Versioning

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )

RESULT

Msg 13525, Level 16, State 1, Line 115
Setting SYSTEM_VERSIONING to ON failed because column ‘StartTime’ has data type datetime in history table ‘SqlhintsTemporalDemoDB.dbo.ProductHistory’ which is different from corresponding column type datetime2(7) in table ‘SqlhintsTemporalDemoDB.dbo.Product’.

From the error it is clear that even the column data types should match in order to enable system versioning

Let us match ProductHistory tables all the columns data types with the corresponding columns in the Product table

--Alter StartTime Column type to DATETIME2
ALTER TABLE dbo.ProductHistory
ALTER COLUMN  [StartTime] DATETIME2 NOT NULL
--Alter EndTime Column type to DATETIME2
ALTER TABLE dbo.ProductHistory
ALTER COLUMN  [EndTime] DATETIME2 NOT NULL
GO

Now try to enable System-Versioning

ALTER TABLE [dbo].[Product]
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory) )

After executing the above statement, if we look into the SSMS window we can see that a dbo.Product table is marked as System-Versioned table. And dbo.ProductHistory table is nested in the dbo.Product table and marked as History Table as shown below.

SMS View of the Temporal Table Product 2
SUMMARY

In summary following are the some of the major list of rules needs to be satified by the existing history table in order for it to be linked by the Temporal table as the history table

  • History Table shouldn’t have Primary Key Constraint
  • History Table shouldn’t have any Foreign key coinstraints
  • History table shouldn’t have any identity column
  • Number of columns in the history table should be same as that of the parent table
  • The columns Ordinal position in the history table should match with the column in the parent table
  • Data type of all the columns in the history tables should match with the columns in the parent table
  • No Triggers/CDC/Change Tracking defined on the History table

Below is the script for enabling System-Versioning for an existing regular table (i.e. dbo.Product) linking it to an existing history table (i.e. dbo.ProductHistory )

BEGIN TRAN
--Add two PERIOD datetime2 columns and PERIOD definition 
ALTER TABLE dbo.Product
ADD StartTime DATETIME2 GENERATED ALWAYS AS ROW START
  HIDDEN NOT NULL DEFAULT GETUTCDATE(),
 EndTime   DATETIME2 GENERATED ALWAYS AS ROW END HIDDEN NOT NULL
  DEFAULT CONVERT(DATETIME2,'9999-12-31 23:59:59.9999999'),
PERIOD FOR SYSTEM_TIME (StartTime, EndTime)
--Enable System Versioning
ALTER TABLE dbo.Product
SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE=dbo.ProductHistory))
COMMIT TRAN

CLEAN-UP

Let us drop the Product and ProductHistory tables by the following script

--Disable the system versioning
ALTER TABLE dbo.Product
    SET (SYSTEM_VERSIONING = OFF)
GO
--Drop Period definition
ALTER TABLE dbo.Product
DROP PERIOD FOR SYSTEM_TIME
GO
--Now drop Product and ProductHistory tables
DROP TABLE dbo.Product
DROP TABLE dbo.ProductHistory

[ALSO READ] New features in Sql Server 2016:

Temporal Tables in Sql Server 2016 Part 2: Querying System-Versioned Temporal Table

Sql Server, Sql Server 2016, , , , , , , , , , , , , , ,

This is the second article in the series of articles on the Temporal Tables, below is the complete list of articles on System-Versioned Temporal Tables. This article covers the querying of the Temporal tables by new temporal querying clause FOR SYSTEM_TIME and its five sub-clauses in the SELECT…FROM construct. This construct simplifies the querying of the History data and hides the complexity from the users. Even though the temporal table data exists in two tables one is the current table and other is the history table, this construct hides all the complexity of fetching data from these two tables.

Let us create a demo database with Temporal Table dbo.Customer with the following script:

CREATE DATABASE SqlHintsQueryingTemporalDB
GO
USE SqlHintsQueryingTemporalDB
GO
CREATE TABLE dbo.Customer 
(  
  Id INT NOT NULL PRIMARY KEY CLUSTERED,
  Name NVARCHAR(100) NOT NULL, 
  StartTime DATETIME2 GENERATED ALWAYS AS ROW START
            HIDDEN NOT NULL,
  EndTime   DATETIME2 GENERATED ALWAYS AS ROW END 
            HIDDEN NOT NULL,
  PERIOD FOR SYSTEM_TIME (StartTime, EndTime)   
) 
WITH(SYSTEM_VERSIONING= ON (HISTORY_TABLE=dbo.CustomerHistory))

The above script will create the Temporal Table dbo.Customer and the corresponding History Table dbo.CustomerHistory as shown in the following image:

SSMS View of Temporal and History Table

Let us populate the data in the temporal table by performing the following DML operations:

INSERT INTO dbo.Customer VALUES (1,'Basavaraj')
GO
WAITFOR DELAY '00:02:00'
GO
UPDATE dbo.Customer SET Name = 'Basavaraj Biradar' WHERE Id = 1
GO
WAITFOR DELAY '00:02:00'
GO
UPDATE dbo.Customer SET Name = 'Basavaraj P Biradar'
WHERE Id = 1
GO
WAITFOR DELAY '00:02:00'
GO
UPDATE dbo.Customer SET Name = 'Basavaraj Prabhu Biradar'
WHERE Id = 1
GO

Here I am keeping a delay of 2 minutes between each DML operations by using the WAITFOR DELAY statement.

Below image shows the records in the dbo.Customer and dbo.CustomerHistory tables after executing the above DML statements:

Records in the Temporal and History Table

Below is the depiction of the above DML operations on the Timeline graph:

System Versioning TimeLine Graph

Now we have the Temporal Table with the sample data, let us start understanding one-by-one the five sub-clauses of Temporal querying clause FOR SYSTEM_TIME:

AS OF <datetime> sub-clause of the temporal querying clause FOR SYSTEM_TIME

This sub-clause returns a record for each row that was valid at the specified point-in-time. In other words it will bring all the records from the Temporal Table and the history table which meet the following criteria:

StartTime<= @PointInTime AND EndTime > @PointInTime

Let us try to get the state of the data that was valid at ‘2015-12-29 07:51’. This point-in-time in the past is depicted in the below milestone graph by Yellow milestone point circle.

FOR SYSTEM_TIME AS OF TimeLine Graph

Execute the following query to get the records which were valid in the past point-in-time ‘2015-12-29 07:51’ by enabling the execution plan

SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
FOR SYSTEM_TIME AS OF '2015-12-29 07:51'

RESULT:
FOR SYSTEM_TIME AS OF Example 1

Below is the execution plan of this query execution.

FOR SYSTEM_TIME AS OF Execution Plan

From the execution plan we can see that the FOR SYSTEM_TIME AS OF clause internally retrieving the data from both the Temporal Table and History Table and returning the UNION of the results from both the tables. One more observation from the execution plan is that on the temporal table we seeing Clustered Index scan, it is because our queries filter predicate is based on the Period columns but we don’t have index on these columns. So if we know that we are going to query by the Period columns it is better to add an index on these columns and by default Sql Server is adding an index on the period columns in the History table.

Below is an equivalent query of this query, which we would have written if this construct was not available:

DECLARE @PointInTime DATETIME = '2015-12-29 07:51'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
WHERE StartTime<= @PointInTime  AND EndTime > @PointInTime 
UNION ALL
SELECT Id, Name, StartTime, EndTime 
FROM dbo.CustomerHistory
WHERE StartTime<= @PointInTime  AND EndTime > @PointInTime

RESULT
Equivalent of FOR SYSTEM_TIME AS OF

FROM <StartDateTime> TO <EndDateTime> sub-clause of the temporal querying clause FOR SYSTEM_TIME

This clause returns all the row versions which were some time active between <StartDateTime> and <EndDateTime> (i.e. all the row versions where StartTime is before the input <EndDateTime> and EndTime after the input parameter <StartDateTime>). In other words it will return all the row versions which match the below criteria:

StartTime < <EndDateTime> AND EndTime > <StartDateTime>

Below is an example of a FROM … TO … clause:

DECLARE @StartDateTime DATETIME = '2015-12-29 07:50',
	@EndDateTime DATETIME = '2015-12-29 07:54'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
FOR SYSTEM_TIME FROM @StartDateTime TO @EndDateTime

RESULT
FOR SYSTEM_TIME FROM TO Example

Below is the execution plan of this query execution.

FOR SYSTEM_TIME FROM TO Execution Plan

From the execution plan we can see that the FOR SYSTEM_TIME FROM … TO … clause internally retrieving the data from both the Temporal Table and History Table which satisfies the criteria and then returning the UNION of the results from both the tables. Below is an equivalent query of this query, which we would have written if this construct was not available:

DECLARE @StartDateTime DATETIME = '2015-12-29 07:50',
	@EndDateTime DATETIME = '2015-12-29 07:54'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
WHERE StartTime < @EndDateTime AND EndTime > @StartDateTime
UNION ALL
SELECT Id, Name, StartTime, EndTime 
FROM dbo.CustomerHistory
WHERE StartTime < @EndDateTime AND EndTime > @StartDateTime

RESULT
Equivalent of FOR SYSTEM_TIME FROM TO

BETWEEN <StartDateTime> AND <EndDateTime> sub-clause of the temporal querying clause FOR SYSTEM_TIME

This clause is same as the previous FROM <StartDateTime> TO <EndDateTime> clause except that it also includes the records which became active on <EndDateTime> (i.e. StartTime = <EndDateTime>). In other words it will return all the row versions which match the below criteria:

StartTime <= <EndDateTime> AND EndTime > <StartDateTime>

Let us execute the below query which is using the BETWEEN clause with the same @StartDateTime AND @EndDateTime as in the FROM clause example

DECLARE @StartDateTime DATETIME = '2015-12-29 07:50',
        @EndDateTime DATETIME = '2015-12-29 07:54'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
FOR SYSTEM_TIME BETWEEN @StartDateTime AND @EndDateTime

RESULT
FOR SYSTEM_TIME BETWEEN AND Example

From the result we can observe that BETWEEN clause is returning one extra record whose StartTime = @EndDateTime compared to the FROM clause

Below is the execution plan of this query execution.
FOR SYSTEM_TIME BETWEEN AND Execution Plan

From the execution plan we can see that the FOR SYSTEM_TIME BETWEEN … TO … clause internally retrieving the data from both the Temporal Table and History Table which satisfies the criteria and then returning the UNION of the results from both the tables. Below is an equivalent query of this query, which we would have written if this construct was not available:

DECLARE @StartDateTime DATETIME = '2015-12-29 07:50',
	@EndDateTime DATETIME = '2015-12-29 07:54'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
WHERE StartTime <= @EndDateTime AND EndTime > @StartDateTime
UNION ALL
SELECT Id, Name, StartTime, EndTime 
FROM dbo.CustomerHistory
WHERE StartTime <= @EndDateTime AND EndTime > @StartDateTime

CONTAINED IN ( <StartDateTime> , <EndDateTime>) sub-clause of the temporal querying clause FOR SYSTEM_TIME

This clause returns only the row versions which became active and ended in the specified date range. In other words it will return all the row versions which match the below criteria:

StartTime >= <StartDateTime> AND EndTime <= <EndDateTime>

Let us execute the below query which is using the CONTAINED clause with the same @StartDateTime AND @EndDateTime which are used in the previous BETWEEN clause example

DECLARE @StartDateTime DATETIME = '2015-12-29 07:50',
	@EndDateTime DATETIME = '2015-12-29 07:54'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
FOR SYSTEM_TIME CONTAINED IN (@StartDateTime, @EndDateTime)

RESULT
FOR SYSTEM_TIME CONTAINED Example
Below is the execution plan of this query execution.
FOR SYSTEM_TIME CONTAINED Execution Plan

From the execution plan we can see that the FOR SYSTEM_TIME CONTAINED IN clause internally retrieving the data from both the Temporal Table and History Table which satisfies the criteria and then returning the UNION of the results from both the tables. Below is an equivalent query of this query, which we would have written if this construct was not available:

DECLARE @StartDateTime DATETIME = '2015-12-29 07:50',
	@EndDateTime DATETIME = '2015-12-29 07:54'
SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
WHERE StartTime >= @StartDateTime AND EndTime <= @EndDateTime
UNION ALL
SELECT Id, Name, StartTime, EndTime 
FROM dbo.CustomerHistory
WHERE StartTime >= @StartDateTime AND EndTime <= @EndDateTime

FOR SYSTEM_TIME ALL

This clause returns all the row versions from both the Temporal and History table

Let us execute the below query which is using the ALL clause:

SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
FOR SYSTEM_TIME ALL

RESULT
FOR SYSTEM_TIME ALL Example
Below is the execution plan of this query execution.
FOR SYSTEM_TIME ALL Execution Plan

From the execution plan we can see that the FOR SYSTEM_TIME ALL clause internally retrieving the data from both the Temporal Table and History Table and returning the UNION of the both the results. Below is an equivalent query of this query, which we would have written if this construct was not available:

SELECT Id, Name, StartTime, EndTime 
FROM dbo.Customer
UNION ALL
SELECT Id, Name, StartTime, EndTime 
FROM dbo.CustomerHistory

[ALSO READ] New features in Sql Server 2016: