Turtle_Jaye的博客

题目链接： https://leetcode.com/problems/swap-salary/题目大意：将‘sex’列中的’f’值替换成’m’,‘m’值替换成’f’.不能使用select关键字。update salary set sex = if(sex = 'f','m','f')利用类似三元运算符来判断即可，上述if语句内的意思是：如果sex = ’ f ‘,取’ m ‘，否则取’ ...

题目链接：https://leetcode.com/problems/duplicate-emails/题目大意：取出重复的Email数据。select Email from Person group by Email having count(*) > 1

题目链接：https://leetcode.com/problems/combine-two-tables/左连接就是按我自己的理解就是取出左表格的列数据与右表格的列数据进行连接，若右表格的某些列是左表格没有的，那取null值select Person.FirstName, Person.LastName, Address.City, Address.State from Person Lef...