595. Big Countries - Detailed Explanation

Problem Statement

You are given a table named World that contains data about various countries. The table has columns such as name (the country's name), continent, area (in square kilometers), population, and possibly gdp. Your task is to write an SQL query that returns the name, population, and area of the countries that are considered "big". A country is defined as big if it meets either one of the following conditions:

• Its area is at least 3,000,000 square kilometers, or
• Its population is at least 250,000,000.

The result should be sorted in ascending order by the country's name.

For example, if the table contains:

Then the query should return (for example):

(Note: Russia and Canada do not meet the "big" criteria in this example because Russia’s population is less than 250 million and Canada’s population is far less, even though their areas are large. The exact output will depend on the actual data in the table.)

Hints

1. Filtering with WHERE Clause:
   Use the WHERE clause to filter rows. You need to select countries where either the area is at least 3,000,000 or the population is at least 250,000,000.

2. Logical Operators:
   Use the OR operator in the WHERE clause to combine the two conditions because a country only needs to meet one of the conditions to be considered big.

3. Sorting the Results:
   The final result should be ordered by the country’s name in ascending order. Use the ORDER BY clause for this.

Detailed Approach

1. Select Required Columns:
   You only need to return name, population, and area.

2. Apply the Filtering Conditions:
   Use the WHERE clause to keep only those rows where:

   • area >= 3000000 OR
   • population >= 250000000

3. Sort the Output:
   Use ORDER BY name to sort the result set by the country name in ascending order.

4. Construct the Query:
   Combine the above steps into a single SQL query.

SQL Query

The final SQL query will look like this:

SELECT name, population, area
FROM World
WHERE area >= 3000000 OR population >= 250000000
ORDER BY name;

Explanation

• SELECT name, population, area:
  This part specifies that you want the output to include only the name, population, and area columns.

• FROM World:
  This specifies the table from which to retrieve the data.

• WHERE area >= 3000000 OR population >= 250000000:
  This condition filters the rows. A country is included if its area is at least 3,000,000 square kilometers or its population is at least 250,000,000.

• ORDER BY name:
  Finally, the result is sorted in ascending order based on the name column.