Home > SQL Server, SQL Server 2016, SQL Server 2017 > Temporal Tables–Simple Guide to implement History Tables using SQL Server 2016/2017–Part 2–Accessing History data

Temporal Tables–Simple Guide to implement History Tables using SQL Server 2016/2017–Part 2–Accessing History data


In previous post, we saw how to create Temporal tables or enable System Versioning on an existing table

In this post, we will review how to access History data

Using below code, we will create simple Temporal table and inserted 5 records and querying both the Main and History table

CREATE TABLE dbo.Demo 
 (    
      DemoID int NOT NULL PRIMARY KEY CLUSTERED  IDENTITY 
    , DemoName varchar(50) NOT NULL  
    , SysStartTime datetime2 GENERATED ALWAYS AS ROW START NOT NULL  
    , SysEndTime datetime2 GENERATED ALWAYS AS ROW END NOT NULL  
    , PERIOD FOR SYSTEM_TIME (SysStartTime,SysEndTime)     
 )    
 WITH (SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.DemoHistory)) 
 ;

INSERT INTO dbo.Demo (DemoName) VALUES ('Demo1') 
 INSERT INTO dbo.Demo (DemoName) VALUES ('Demo2') 
 INSERT INTO dbo.Demo (DemoName) VALUES ('Demo3') 
 INSERT INTO dbo.Demo (DemoName) VALUES ('Demo4') 
 INSERT INTO dbo.Demo (DemoName) VALUES ('Demo5')

SELECT DemoID, 
        DemoName, 
        SysStartTime, 
        SysEndTime FROM dbo.Demo

SELECT DemoID, 
        DemoName, 
        SysStartTime, 
        SysEndTime FROM dbo.DemoHistory

 

Output: Main table has 5 rows and and History has no data, because no changes were made yet to the data, Also if you notice the SysEndTime, all of them are set to 12/31/9999 23:59:59.9999999, which refer to them as current record

capture20171020104246809

Let us modify some data in 2 minute intervals

First Change – Update 1 row and delete 1 row

UPDATE dbo.Demo 
    SET DemoName='Demo11' 
    WHERE DemoID=1

DELETE FROM dbo.Demo WHERE DemoID=4

Output: Now we can see that Main table has 4 rows and History has 2 rows , the green highlighted is the record we updated as you can history table contains the previous version of record and also SysEndTime in History table indicates when it was updated

Similarly Red highlighted record in history is the deleted with Deleted time

capture20171020104303651

Second Update: Update 1 record and Delete 1 record

UPDATE dbo.Demo 
    SET DemoName='Demo12' 
    WHERE DemoID=2

DELETE FROM dbo.Demo WHERE DemoID=3

Output:

capture20171020121832704

Let us now review how we can access the History data

Method 1: AS OF

We can use FOR SYSTEM_TIME AS OF to get records in Demo as of the specific time, This will be helpful for scenarios when you want to see How much Inventory was in hand as of a particular date and time or What products were in hand as of particular date and time

In below example we are using 3 different time with 2 minute intervals

SELECT DemoID, 
       DemoName, 
       SysStartTime, 
        SysEndTime FROM dbo.Demo 
    FOR SYSTEM_TIME AS OF '2017-10-20 14:42:34' 
    ORDER BY DemoID

SELECT DemoID, 
       DemoName, 
       SysStartTime, 
       SysEndTime FROM dbo.Demo 
    FOR SYSTEM_TIME AS OF '2017-10-20 14:44:34' 
    ORDER BY DemoID

SELECT DemoID, 
       DemoName, 
        SysStartTime, 
       SysEndTime FROM dbo.Demo 
    FOR SYSTEM_TIME AS OF '2017-10-20 14:46:34' 
    ORDER BY DemoID

Output: As we can see in first output we are able to see all records as how it was inserted and in 2nd put, we can see 1st record was updated and Demo ID 4 record is missing and in output 3 23 can seem Demo ID 1 and 2 are updated and 3 and 4 are deleted

capture20171020122217154

Method 2: FROM…TO and  BETWEEN…AND option

We can use FROM…TO and BETWEEN…AND option to get records changed between 2 specified date times

SELECT DemoID, 
       DemoName, 
       SysStartTime, 
       SysEndTime 
    FROM dbo.Demo 
    FOR SYSTEM_TIME FROM '2017-10-20 14:42:33' TO '2017-10-20 14:46:55' 
    ORDER BY DemoID, SysStartTime

SELECT DemoID, 
        DemoName, 
       SysStartTime, 
       SysEndTime 
    FROM dbo.Demo 
    FOR SYSTEM_TIME BETWEEN '2017-10-20 14:42:33' AND '2017-10-20 14:46:55' 
    ORDER BY DemoID, SysStartTime

 

Output: In below output you can see all changes made between the specified time intervals, but if you notice it, its providing us both version of the records, so based on your application need, you will need to use this or else, it might provide more records for display than you need

capture20171020123046024

Method 3: CONTAINED IN

When we use CONTAINED IN option, it provides data from history table only for the specified datetime(s)

SELECT DemoID, 
        DemoName, 
        SysStartTime, 
       SysEndTime 
    FROM dbo.Demo 
    FOR SYSTEM_TIME CONTAINED IN ('2017-10-20 14:42:33', '2017-10-20 14:45:56') 
    ORDER BY DemoID, SysStartTime

 

Output: As we can see the below output doesn’t contain the current version of record or other records from Main table

capture20171020123430862

Method 4: ALL

When we use ALL option, it provides data from both Main and History table for all the changes made so far

SELECT DemoID, 
        DemoName, 
        SysStartTime, 
       SysEndTime FROM dbo.Demo 
    FOR SYSTEM_TIME ALL 
    ORDER BY DemoID, SysStartTime

Output

We can see all records from main and history table combined, Please be cautious using this option when running without Filter criteria for larger tables

capture20171020123659353

We can create Views using Temporal Tables and those views supports these clauses as well

Hope you find this post helpful !!!

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