mysql数据库优化课程---10.mysql数据库分组聚合 一.总结 一句话总结:select concat(class,' 班') 班级,concat(count(*),' 人') 人数 from user group by class; select class,max(id),min(id),count(*),sum(id),avg(id) from user group by class; count(*) group by class 1.为什么操作系统要选择linux? 很多开源产…
给定 n 个点和 m 条边的一张图和一个值 k ,求图中边数为 k 的联通子图个数 mod 1e9+7. \(n \le 10^5, m \le 2 \times 10^5, 1 \le k \le 4\). 观察到 k 的值贼小,考虑分类讨论 下面代码中du[]代表点的度数.(度 找不到比较好的英文,而这个拼音比较巨,所以du是我的代码习惯中里出现拼音的少数几中情况之一)…
实例1: SET @ID = 0; SELECT AVG(loan_amount) from ( SELECT @ID:=@ID+1 as ID, loan_amount FROM table_xxx ORDER BY loan_amount ) a where IF( ROUND(@ID/2,0)%2=0,ID in (ROUND(@ID/2,0),ROUND(@ID/2,0)/2 + 1), ID=ROUND(@ID/2,0) ) 实例2: SET @ID = 0; SELECT AVG…
题目: There are two sorted arrays nums1 and nums2 of size m and n respectively. Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Subscribe to see which companies asked this question 解题思路: 我自己想的方法,先排序在查找.…
