How to use Window Functions In SQL

Window functions in PostgreSQL allow for performing calculations across a set of rows related to the current row. By utilizing window functions, you can compute the delta between values in two columns on different rows.

SELECT 
    value,
    value - LAG(value) OVER (ORDER BY id) AS delta
FROM 
    example_table;

Explanation:

• SELECT value, value – LAG(value) OVER (ORDER BY id) AS delta: This part of the query selects the value column from the example_table and calculates the difference (delta) between the current value and the previous value using the LAG window function.
• value: This selects the value column from the example_table.
• LAG(value) OVER (ORDER BY id): This part calculates the value of the value column from the previous row, ordered by the id column. The LAG function retrieves the value from the previous row based on the specified ordering. If there’s no previous row, it returns NULL.
• value – LAG(value) OVER (ORDER BY id) AS delta: This computes the difference (delta) between the current value and the previous value, and aliases the result as delta.
• FROM example_table: This specifies the table from which the value column is selected.

Output:

In PostgreSQL the modern relational database system, two types of queries are supported: SQL for the traditional relational databases and JSON for the non-relational databases. It is free and anybody can use it. The difference (delta) computation between the values of two columns of PostgreSQL at different rows can be done with various techniques.

In data manipulation and data analysis tasks, the numerical values on different rows in two columns are often compared. The difference (delta) is computed to do such a comparison. This article explores various techniques to achieve this task efficiently and effectively.