SQL LAST_VALUE with auditing

29 Sep 2023

Auditing

SQL LAST_VALUE is a powerful analytical function that allows you to retrieve the last value in a specified column within a group. This function can be particularly useful when you need to audit changes made to a specific field in your database table. In this article, we will explore how to use SQL LAST_VALUE with auditing.

Understanding the LAST_VALUE Function

The LAST_VALUE function in SQL returns the last value in an ordered set of rows. It is commonly used for calculations such as running totals, cumulative sums, and tracking changes over time. The function takes two arguments - the column from which you want to retrieve the last value and the sort order.

LAST_VALUE(column) OVER (ORDER BY sort_columns [ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW])

Setting Up an Auditing Table

To demonstrate how to use SQL LAST_VALUE with auditing, let’s create a simple table to track changes made to a specific field in our database. We will call this table “audit_log” and include the following columns:

id: the unique identifier for each audit log entry
record_id: the identifier of the record being audited
field_name: the name of the field being audited
old_value: the previous value of the field
new_value: the current value of the field
audit_timestamp: the timestamp of the audit log entry

CREATE TABLE audit_log (
    id INT PRIMARY KEY,
    record_id INT,
    field_name VARCHAR(255),
    old_value VARCHAR(255),
    new_value VARCHAR(255),
    audit_timestamp TIMESTAMP
);

Using LAST_VALUE for Auditing

Now that we have our audit_log table set up, let’s use the SQL LAST_VALUE function to audit changes made to a specific field in another table called “records”. We will track changes made to the “status” field.

SELECT DISTINCT
    record_id,
    field_name,
    LAST_VALUE(new_value) OVER (PARTITION BY record_id, field_name ORDER BY audit_timestamp) AS last_status,
    audit_timestamp
FROM audit_log
WHERE field_name = 'status'
ORDER BY record_id, audit_timestamp;

In the above query, we use the PARTITION BY clause to group the audit log entries by record_id and field_name. Then, we use the ORDER BY clause to order the audit log entries by the audit_timestamp. Finally, we apply the LAST_VALUE function to retrieve the last status value for each record.

This query will return a result set displaying the record_id, field_name, last_status value, and audit_timestamp for each audit log entry where the field_name is ‘status’.

Conclusion

SQL LAST_VALUE is a powerful function when it comes to auditing changes made to specific fields within a database table. By leveraging the LAST_VALUE function, you can easily track and retrieve the last value for a given field and perform auditing tasks efficiently.

#SQL #Auditing