Question

SELECT p1.country_code,

p1.size AS size2010,
p2.size AS size2015
FROM populations AS p1
INNER JOIN populations AS p2
ON p1.country_code = p2.country_code
AND p1.year = p2.year - 5;

Answer 1

The SQL statement is for comparing the size of a country's population between the years 2010 and 2015 by joining the same table on country_code and year with a 5-year interval.

Step-by-step explanation:

The SQL statement provided in the question is designed to join records from the same 'populations' table based on a condition that relates two sets of population data from different years, specifically data 5 years apart (size2010 vs. size2015). The INNER JOIN is used to combine rows from both sets where the 'country_code' matches and where the 'year' of the first dataset (aliased as p1) is 5 years earlier than the year in the second dataset (aliased as p2). This allows for a comparison of the population sizes of countries between the two years. The 'populations' table contains population data for different countries, which can include the population size, the country_code, and the year the data was recorded.