【Leetcode】595. Big Countries（Easy）-优快云博客

本文链接：https://blog.youkuaiyun.com/Crab0314/article/details/79651269

本文介绍了一个SQL查询案例，通过使用union操作符结合两个条件来筛选出面积大于3百万平方公里或人口超过2500万的大国。

1.题目

There is a table World

+-----------------+------------+------------+--------------+---------------+
| name            | continent  | area       | population   | gdp           |
+-----------------+------------+------------+--------------+---------------+
| Afghanistan     | Asia       | 652230     | 25500100     | 20343000      |
| Albania         | Europe     | 28748      | 2831741      | 12960000      |
| Algeria         | Africa     | 2381741    | 37100000     | 188681000     |
| Andorra         | Europe     | 468        | 78115        | 3712000       |
| Angola          | Africa     | 1246700    | 20609294     | 100990000     |
+-----------------+------------+------------+--------------+---------------+

A country is big if it has an area of bigger than 3 million square km or a population of more than 25 million.

Write a SQL solution to output big countries' name, population and area.

For example, according to the above table, we should output:

+--------------+-------------+--------------+
| name         | population  | area         |
+--------------+-------------+--------------+
| Afghanistan  | 25500100    | 652230       |
| Algeria      | 37100000    | 2381741      |
+--------------+-------------+--------------+

翻译：有一个表叫World。如果一个国家占地面积超过300万平方千米或者有超过2,500万的人口，那么就称这个这个国家是大国。现在写一个SQL查询语句，输出大国的名字，人口和占地面积。

2.思路

或连接的两个条件，用union连接。

3.算法

(select name,population,area from World
where area>3000000)
union
(select name,population,area from World
where population>25000000)

4.总结

where .. and ... 是要求同时满足两个条件。 select多少属性，都是用逗号连接，而不是用and