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文章目录一、code1.1 题目描述1.2 题解二、总结一、code1.1 题目描述地址1.2 题解# Write your MySQL query statement belowselect id, case when p_id is null then 'Root' when id in (select distinct p_id from tree) then 'Inner' # 当not in（） 里面包含null值，查询不会返回任何值

文章目录一、code1.1 题目描述1.2 题解二、总结一、code1.1 题目描述Leetcode地址1.2 题解# Write your MySQL query statement belowselect a.request_at 'Day',round(sum(if(a.status = 'completed',0,1))/count(*), 2) 'Cancellation Rate'from ( select request_at, s

文章目录一、code1.1 题目描述1.2 题解二、总结一、code1.1 题目描述Leetcode地址1.2 题解select dep.name Department, a.name Employee, a.salary Salaryfrom Department dep join (select departmentId, name, salary, dense_rank() over(partition by depa

文章目录一、code1.1 题目描述1.2 题解二、总结一、code1.1 题目描述Leetcode地址1.2 题解select distinct # 去重 l1.num as ConsecutiveNumsfrom Logs l1, Logs l2, Logs l3where l1.id + 1 = l2.id # 连续三个 and l2.id = l3.id - 1 and l1.num = l2.num # 值相同

文章目录一、code二、知识点rank函数一、codeLeetcode:178 分数排名# Write your MySQL query statement belowselect score, dense_rank() over(order by score desc) as 'rank' # 这个rank之所以要加引号，因为rank本身是个函数，直接写rank会报错from Scores;二、知识点rank函数rank()： 对查询数据进行排序，值相同的排序后序号也会相同，注意r

文章目录一、code一、codeLeetcode:177 第N高的薪水CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INTBEGIN declare m INT; SET M = N - 1; RETURN ( # Write your MySQL query statement below. select ifnull((select distinct salary as getNth

文章目录一、code二、知识点1.ifnull2.limit与offset用法一、codeselect ifnull((select distinct salary from employee order by salary desc limit 1 offset 1), null) as SecondHighestSalary;二、知识点1.ifnullifnull() 函数用于判断第一个表达式是否为NULL，如果为NULL则返回第二个