Computing a Difference (Delta) Between Two Columns on Different Rows
Three distinct methods will be explored in detail:
Using Window Functions
Window functions in PostgreSQL offer a robust mechanism for performing calculations across a set of rows relative to the current row. Leveraging these functions, we can easily compute the delta between values in two columns on different rows.
Using Subqueries
Another approach involves utilizing subqueries to retrieve the values of the previous row and then calculating the delta. This method provides flexibility and is particularly useful in scenarios where window functions may not be applicable.
Using Common Table Expressions (CTEs)
Common Table Expressions (CTEs) allow for defining temporary result sets that can be referenced within a query. By leveraging CTEs, we can efficiently compute the delta between values in two columns on different rows while maintaining readability and manageability.
First, we’ll create a table named example_table with two columns: id, and value.
CREATE TABLE example_table (
id SERIAL PRIMARY KEY,
value INTEGER
);
Now, let’s insert some sample data into the table:
INSERT INTO example_table (value) VALUES (10), (20), (30), (40), (50);
Now our table is ready, and we have some sample data. Here are some examples of computing the difference (or delta) between the value columns of different rows.
Compute a Difference (Delta) Between Two Columns on Different Rows in postgreSQL
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.
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