一、MySQL.pratice.search

MySQL是一种常用的关系型数据库管理系统，广泛应用于各种Web应用程序中。在编程中，使用MySQL进行数据操作是非常常见的操作。在MySQL中，查询是最常用的操作之一，可以查询整个表或者根据特定的条件查询数据。

一、查询
- （一）[1757. 可回收且低脂的产品](https://leetcode.cn/problems/recyclable-and-low-fat-products/description/?envType=study-plan-v2&envId=sql-free-50)
- （二）[84. 寻找用户推荐人](https://leetcode.cn/problems/find-customer-referee/description/?envType=study-plan-v2&envId=sql-free-50)
- （三）[595. 大的国家](hhttps://leetcode.cn/problems/big-countries/?envType=study-plan-v2&envId=sql-free-50)
- （四）[1148. 文章浏览 I](https://leetcode.cn/problems/article-views-i/description/?envType=study-plan-v2&envId=sql-free-50)
- （五）[1683. 无效的推文](https://leetcode.cn/problems/article-views-i/description/?envType=study-plan-v2&envId=sql-free-50)

一、查询

select product_id from Products where low_fats = 'Y' and recyclable = 'Y';

select name from customer where referee_id != 2 or referee_id is null;

# Write your MySQL query statement below
select name,population,area from World where population >= 25000000 or area >= 3000000;

# Write your MySQL query statement below
select distinct author_id id from Views where author_id = viewer_id order by id;

# Write your MySQL query statement below
select tweet_id from Tweets where char_length(content) > 15;