mysql world database: select country with max population

Finding the Most Populous Country in MySQL's World Database

Learn how to query the MySQL World database to identify the country with the highest population using SQL, exploring various methods and their efficiency.

The MySQL World database is a classic example dataset often used for learning and demonstrating SQL queries. It contains information about countries, cities, and languages. A common task for beginners and experienced users alike is to find specific data points, such as the country with the maximum population. This article will guide you through different SQL approaches to achieve this, focusing on clarity and efficiency.

Understanding the World Database Schema

Before we dive into queries, it's essential to understand the relevant table structure. The Country table in the World database holds information about each country, including its Name and Population. We'll primarily be working with this table.

erDiagram
    Country ||--o{ City : "has"
    Country ||--o{ CountryLanguage : "speaks"
    Country {
        CHAR Code PK
        CHAR Name
        CHAR Continent
        REAL SurfaceArea
        INT Population
        SMALLINT LifeExpectancy
        DECIMAL GNP
        CHAR HeadOfState
    }
    City {
        INT ID PK
        CHAR Name
        CHAR CountryCode FK
        CHAR District
        INT Population
    }
    CountryLanguage {
        CHAR CountryCode PK,FK
        CHAR Language PK
        ENUM IsOfficial
        REAL Percentage
    }

Simplified Entity-Relationship Diagram for the MySQL World Database

Method 1: Using ORDER BY and LIMIT

The most straightforward way to find the country with the maximum population is to sort all countries by their population in descending order and then retrieve only the top record. This method is generally efficient for this specific task.

SELECT Name, Population
FROM Country
ORDER BY Population DESC
LIMIT 1;

SQL query to find the country with the highest population using ORDER BY and LIMIT.

Method 2: Using a Subquery with MAX()

Another approach involves using a subquery to first determine the maximum population value across all countries, and then selecting the country (or countries, in case of a tie) that matches this maximum population. This method explicitly finds the maximum value first.

SELECT Name, Population
FROM Country
WHERE Population = (SELECT MAX(Population) FROM Country);

SQL query to find the country with the highest population using a subquery and MAX().

Method 3: Using a Common Table Expression (CTE) - MySQL 8.0+

For MySQL 8.0 and newer versions, Common Table Expressions (CTEs) offer a more structured and often more readable way to write complex queries. We can use a CTE to rank countries by population and then select the top-ranked one.

WITH RankedCountries AS (
    SELECT 
        Name, 
        Population,
        ROW_NUMBER() OVER (ORDER BY Population DESC) as rn
    FROM 
        Country
)
SELECT 
    Name, 
    Population
FROM 
    RankedCountries
WHERE 
    rn = 1;

SQL query using a CTE and window function to find the country with the highest population.