How Can I Efficiently Find the Most Frequent Value in One Column for Each Unique Value in Another Column Using SQL?

Finding the Most Common Value for Each Value in Another Column in SQL

When working with tabular data, it is often necessary to identify the most frequently occurring values for a particular column. In the context of SQL, this can be achieved using a variety of methods.

Conventional Approach:

One common approach is to utilize a series of intermediate steps, as demonstrated in the question. This involves creating temporary tables to count occurrences, identify maximum values, and group results appropriately. While this method is functional, it can be cumbersome and prone to errors.

Elegant Solution:

Modern versions of SQL, such as PostgreSQL 9.4 and later, offer simplified solutions for this task. The mode() function returns the most common value within a specified group. This eliminates the need for complex aggregation and manipulation.

Example:

Consider the following table:

To find the food that is eaten most often for each country, we can use the following query:

select mode() within group (order by food_id)
from munch
group by country

This query directly returns the mode for each country, providing a more straightforward and efficient approach.

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