MySQL基础练习题48-连续出现的数字

目录

题目

准备数据

分析数据

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题目

找出所有至少连续出现三次的数字。

准备数据

## 创建库
create database db;
use db;

## 创建表
Create table If Not Exists Logs (id int, num int)

## 向表中插入数据
Truncate table Logs
insert into Logs (id, num) values ('1', '1')
insert into Logs (id, num) values ('2', '1')
insert into Logs (id, num) values ('3', '1')
insert into Logs (id, num) values ('4', '2')
insert into Logs (id, num) values ('5', '1')
insert into Logs (id, num) values ('6', '2')
insert into Logs (id, num) values ('7', '2')

分析数据

1 是唯一连续出现至少三次的数字。

遇见连续性问题，需要两列差值相同的，最后进行相减，相同的即为连续。

第一步：根据num分组，id排序进行排名

select *,
       row_number() over (partition by num order by id) rn
from logs;

第二步：算差值，将id列减去rn列的值

with t1 as (
    select *,
           row_number() over (partition by num order by id) rn
    from logs
) select *,
         (id - cast(rn as signed)) as diff
from t1;

注意：rn列需要强制性转化

with t2 as (
    with t1 as (
        select *,
               row_number() over (partition by num order by id) rn
        from logs
    ) select *,
             (id - cast(rn as signed)) as diff
    from t1
) select
    distinct t2.num as ConsecutiveNums
from t2
group by t2.num,t2.diff
having count(t2.diff) >= 3;