In the realm of database management systems, IBM DB2 offers a hidden gem that often goes unnoticed: temporal tables. This powerful functionality provides a systematic approach to track and manage historical data changes within DB2. In this technical blog, we will dive deep into temporal tables, explore their features, and demonstrate their usage through practical examples.
What are Temporal Tables?
Temporal tables in DB2 allow for the precise tracking of data validity over time. By associating a time period with each row, temporal tables enable effective management of historical data changes. This functionality is divided into two types: system-period temporal tables and application-period temporal tables.
- System-Period Temporal Tables in DB2 automatically manage the validity period of data using system-generated timestamps. This approach simplifies the process of tracking changes. Let's explore how to create and work with system-period temporal tables through an example:
Consider a table named "Employees" with columns such as "ID," "Name," "Department," and "ValidTimeStart" and "ValidTimeEnd" hidden system-generated timestamp columns. We can create a system-period temporal table using the following SQL statement:
CREATE TABLE Employees (
ValidTimeStart TIMESTAMP GENERATED ALWAYS AS ROW BEGIN,
ValidTimeEnd TIMESTAMP GENERATED ALWAYS AS ROW END
) WITH SYSTEM VERSIONING;
Now, when inserting data into the "Employees" table, DB2 will automatically populate the hidden timestamp columns to track the validity period of each row.
- Application-Period Temporal Tables provide more control over the validity period by allowing explicit specification of start and end timestamps for each row. This enables custom-defined validity periods based on specific business logic. Let's look at an example of creating and utilizing an application-period temporal table:
Suppose we have a table called "Sales" with columns like "ID," "Product," "Quantity," and "ValidFrom" and "ValidTo" columns to denote the validity period. We can create an application-period temporal table using the following SQL statement:
CREATE TABLE Sales (
PERIOD FOR Validity (ValidFrom, ValidTo)
) WITH APPEND;
By defining the "Validity" period using the "ValidFrom" and "ValidTo" columns, we can explicitly set the validity period for each row based on our specific requirements.
Querying Temporal Tables:
DB2 provides specialized SQL syntax to query temporal tables and retrieve data based on its validity period. Let's explore some examples:
Example 1: Retrieve current data
To retrieve the current data from a temporal table, use the "FOR SYSTEM_TIME AS OF" clause with the current timestamp:
SELECT * FROM Employees FOR SYSTEM_TIME AS OF CURRENT_TIMESTAMP;
Example 2: Retrieve historical data
To retrieve historical data at a specific point in time, use the "FOR SYSTEM_TIME BETWEEN" clause:
SELECT * FROM Sales FOR SYSTEM_TIME BETWEEN '2023-01-01' AND '2023-03-31';
Example 3: Track changes over time
To track changes over time, use the "VERSIONS BETWEEN" clause to specify a time range:
SELECT * FROM Employees VERSIONS BETWEEN '2022-01-01' AND '2023-01-01';
To keep in mind
Temporal tables in DB2 provide a powerful solution for managing historical data changes with ease. By utilizing system-period and application-period temporal tables, you can precisely track data validity over time and access historical information effortlessly. This blog has demonstrated the creation and usage of temporal tables through practical examples, showcasing their potential for enhancing data analysis, reporting, and historical insights within DB2.
By leveraging the capabilities of temporal tables, developers, analysts, and database administrators can unlock new possibilities in managing and analyzing historical data within DB2, ultimately empowering organizations to make informed decisions based on a rich historical context.