1. 现象与问题 ORDER BY排序后,用LIMIT取前几条,发现返回的结果集的顺序与预期的不一样 下面是我遇到的问题: 可以看到,带LIMIT与不带LIMIT的结果与我预期的不一样,而且“很不可思议”,真是百思不得其解 后来百度了一下,如果order by的列有相同的值时,mysql会随机选取这些行,为了保证每次都返回的顺序一致可以额外增加一个排序字段(比如:id),用两个字段来尽可能减少重复的概率 于是,改成 order by status, id; 问题虽然是解决了,但还是看看官方文档
table: id tag status a b c d 一.group by用法 .与count 联合计数 select status,count(*) from table group by status status count(*)0 21 2 .与 group_concat联合使用 select status,group_concat(tag) as tag from table group by status status tag0 a,b1 c,d 二.limit用法 .分页 设页
这两天由于一位实习生同事回学校答辩,因此我来跟进他之前开发的功能进行测试,测试反馈上来这么一个问题: 也就是说下面这两条sql查询出来的数据前10条的数据不一样. select * from table WHERE display_status = '1' order by update_time desc LIMIT 20; select * from table WHERE display_status = '1' order by update_time desc LIMIT 10; 查看
The k-th Largest Group Time Limit: 2000MS Memory Limit: 131072K Total Submissions: 8807 Accepted: 2875 Description Newman likes playing with cats. He possesses lots of cats in his home. Because the number of cats is really huge, Newman wants to g
mysql group replication,组复制,提供了多写(multi-master update)的特性,增强了原有的mysql的高可用架构.mysql group replication基于mysql插件架构实现,本身就是一个mysql插件. 提供的特性: 多写,写冲突检测 良好的扩展能力,可动态增删节点,组成员自动管理 组内高可用 确保组内数据最终一致性[重要](通过分布式协议和分布式recovery机制保证) 1. 架构 组复制基于mysql插件架构实现,本身作为一个mysql插
传送门 The k-th Largest Group Time Limit: 2000MS Memory Limit: 131072K Total Submissions: 8690 Accepted: 2847 Description Newman likes playing with cats. He possesses lots of cats in his home. Because the number of cats is really huge, Newman wants
The k-th Largest Group Time Limit: 2000MS Memory Limit: 131072K Total Submissions: 8353 Accepted: 2712 Description Newman likes playing with cats. He possesses lots of cats in his home. Because the number of cats is really huge, Newman wants to g
Group Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 208 Accepted Submission(s): 122 Problem Description There are n men ,every man has an ID(1..n).their ID is unique. Whose ID is i and i-1
题目链接: http://codeforces.com/problemset/problem/533/B B. Work Group time limit per test2 secondsmemory limit per test256 megabytes 问题描述 One Big Software Company has n employees numbered from 1 to n. The director is assigned number 1. Every employee of
Group Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 17 Accepted Submission(s): 5 Problem Description There are n men ,every man has an ID(1..n).their ID is unique. Whose ID is i and i-1 are
Group Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 546 Accepted Submission(s): 299 Problem Description There are n men ,every man has an ID(1..n).their ID is unique. Whose ID is i and i-1
