摘要：https://leetcode.com/problems/delete-duplicate-emails/description/ 邮件地址表： + + + | Id | Email | + + + | 1 | a@b.com | | 2 | c@d.com | | 3 | a@b.com | + 阅读全文

摘要：https://leetcode.com/problems/classes-more-than-5-students/description/ + + + | student | class | + + + | A | Math | | B | English | | C | Math | | D 阅读全文

摘要：https://leetcode.com/problems/not-boring-movies/description/ X市开了一家新电影院，很多人都想去这家电影院。电影院还会发布一张海报，说明电影的评级和描述。 请编写一个SQL查询来输出具有奇数编号ID和非“无聊”描述的电影。按评级订购结果。 阅读全文

摘要：https://leetcode.com/problems/swap-salary/description/ | id | name | sex | salary | | | | | | | 1 | A | m | 2500 | | 2 | B | f | 1500 | | 3 | C | m | 阅读全文

摘要：https://leetcode.com/problems/big-countries/description/ 要求： + + + + + + | name | continent | area | population | gdp | + + + + + + | Afghanistan | As 阅读全文