在列中查找N个最大元素

Question

I have a city table comprising of fields such as ID , Name , CountryCode and Population . I want to find the top N(say N = 5) cities with the largest Population .

A very naive way would be to find the city with the largest population using the MAX() group function, and finding the rest via a variant of the method mentioned here.

What is the simplest SQL Query to find the second largest value?

Does anyone know of a better method to achieve the goal?

Answer 1

If you just want the top N cities, using order by and limit would be a much simpler approach:

SELECT   *
FROM     city
ORDER BY population DESC
LIMIT    5 -- or any other N

Answer 2

SELECT *
FROM cities AS c1
WHERE
(SELECT COUNT(*)
 FROM cities AS c2
 WHERE c2.population > c1.population)<5;

This query may return more than five rows if there are several cities with the same population. You didn't specify what result you expect for "top 5" when there are tied values.