Show All Rows with an Above-Average Value in PostgreSQL

PostgreSQL is a powerful relational database management system renowned for its robust features suitable for extensive data analysis tasks. One common requirement in data analytics is to identify and display rows where certain column values exceed the column's average.

This article looks into three effective methods to achieve this in PostgreSQL: Subqueries, Window Functions, and Common Table Expressions (CTEs).

How to Show All Rows with an Above-Average Value in PostgreSQL?

When working with databases, it is often necessary to filter rows based on certain conditions. In this case, we want to show all rows where a specific column value is above the average of that column. PostgreSQL provides several methods to solve this problem. below are the methods that help us to show All Rows with an Above-Average Value in PostgreSQL are as follows:

Setting Up the Environment

To understand how to Show All Rows with an Above-Average Value in PostgreSQL we need a table on which we will perform various operations and queries. Here we will consider a table called sales_data with columns transaction_id, product_name, and amount to represent sales transactions:

CREATE TABLE sales_data (
    transaction_id SERIAL PRIMARY KEY,
    product_name VARCHAR(100),
    amount NUMERIC
);
INSERT INTO sales_data (product_name, amount) VALUES
    ('Product A', 1500),
    ('Product B', 2200),
    ('Product C', 1800),
    ('Product D', 1300),
    ('Product E', 2500);

Output:

1. Using Subqueries

Let's retrieve all records from the 'sales_data' table where the 'amount' is greater than the average amount in the 'sales_data' table.

Query:

SELECT *FROM sales_data
WHERE amount > (SELECT AVG(amount) 
FROM sales_data);

Output:

Explanation: This query retrieves all columns from the 'sales_data' table for rows where the 'amount' is greater than the average amount in the 'sales_data' table.

2. Using Window Functions

Let's retrieve all records from the 'sales_data' table where the 'amount' is greater than the average amount in the 'sales_data' table for each row.

Query:

SELECT *, AVG(amount) OVER () AS average_amount
FROM sales_data
WHERE amount > average_amount;

Output:

Explanation: This query calculates the average amount from the sales_data table using the AVG window function and then selects all columns from the 'sales_data' table where the 'amount' is greater than this average amount.

3. Using Common Table Expressions (CTE)

Let's retrieve all records from the 'sales_data' table where the 'amount' is greater than the average amount calculated using a Common Table Expression (CTE) named 'average_cte'.

Query:

WITH average_cte AS (
    SELECT AVG(amount) AS average_amount
    FROM sales_data
)
SELECT * FROM sales_data
JOIN average_cte ON true
WHERE amount > average_amount;

Output:

Explanation: This query calculates the average amount from the 'sales_data' table using a Common Table Expression (CTE) named 'average_cte' and then joins the 'sales_data' table with the 'average_cte' to filter and select all rows where the 'amount' is greater than the average amount.

Conclusion

Overall, in this article, we have understand the three approaches to showing all rows with an above-average value in PostgreSQL. By using the method like subqueries, window functions, and Common Table Expressions you can efficiently filter rows based on specific conditions and gain valuable insights from your data.