MySQL练手题--日期连续类型（困难）

一、准备工作

Create table If Not Exists Failed (fail_date date);
Create table If Not Exists Succeeded (success_date date);
Truncate table Failed;
insert into Failed (fail_date) values ('2018-12-28');
insert into Failed (fail_date) values ('2018-12-29');
insert into Failed (fail_date) values ('2019-01-04');
insert into Failed (fail_date) values ('2019-01-05');
Truncate table Succeeded;
insert into Succeeded (success_date) values ('2018-12-30');
insert into Succeeded (success_date) values ('2018-12-31');
insert into Succeeded (success_date) values ('2019-01-01');
insert into Succeeded (success_date) values ('2019-01-02');
insert into Succeeded (success_date) values ('2019-01-03');
insert into Succeeded (success_date) values ('2019-01-06');

表：Failed

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| fail_date    | date    |
+--------------+---------+
该表主键为 fail_date (具有唯一值的列)。
该表包含失败任务的天数.

表： Succeeded

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| success_date | date    |
+--------------+---------+
该表主键为 success_date (具有唯一值的列)。
该表包含成功任务的天数.

系统每天运行一个任务。每个任务都独立于先前的任务。任务的状态可以是失败或是成功。

编写解决方案找出 2019-01-01 到 2019-12-31 期间任务连续同状态 period_state 的起止日期（start_date 和 end_date）。即如果任务失败了，就是失败状态的起止日期，如果任务成功了，就是成功状态的起止日期。

最后结果按照起始日期 start_date 排序

返回结果样例如下所示:

示例 1：

输入：
Failed table:
+-------------------+
| fail_date         |
+-------------------+
| 2018-12-28        |
| 2018-12-29        |
| 2019-01-04        |
| 2019-01-05        |
+-------------------+
Succeeded table:
+-------------------+
| success_date      |
+-------------------+
| 2018-12-30        |
| 2018-12-31        |
| 2019-01-01        |
| 2019-01-02        |
| 2019-01-03        |
| 2019-01-06        |
+-------------------+
输出：
+--------------+--------------+--------------+
| period_state | start_date   | end_date     |
+--------------+--------------+--------------+
| succeeded    | 2019-01-01   | 2019-01-03   |
| failed       | 2019-01-04   | 2019-01-05   |
| succeeded    | 2019-01-06   | 2019-01-06   |
+--------------+--------------+--------------+
解释：
结果忽略了 2018 年的记录，因为我们只关心从 2019-01-01 到 2019-12-31 的记录
从 2019-01-01 到 2019-01-03 所有任务成功，系统状态为 "succeeded"。
从 2019-01-04 到 2019-01-05 所有任务失败，系统状态为 "failed"。
从 2019-01-06 到 2019-01-06 所有任务成功，系统状态为 "succeeded"。

二、分析

三、实现

with t as (                      --  连接两张表select 'succeeded' as period_state,success_date date from succeeded
union allselect 'failed' as failed,fail_date date from failed
), t1 as (                     select                       -- 对日期排序并筛选2019年时间*,row_number() over (partition by period_state order by date) rnfrom t where date between '2019-01-01' and '2019-12-31'
), t2 as (select*,date - INTERVAL rn DAY rn1   -- 时间与排序做差值，时间减去rn相应天数，时间相同的为连续from t1
), t3 as (selectperiod_state,min(date) start_date,     -- 开始时间max(date) end_date,       -- 结束时间rn1 from t2 group by period_state,rn1
)
select period_state,start_date,end_date from t3 order by start_date;