1225. Report Contiguous Dates

https://leetcode.com/problems/report-contiguous-dates

Description

Table: Failed

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| fail\_date    | date    |
+--------------+---------+
Primary key for this table is fail\_date.
Failed table contains the days of failed tasks.

Table: Succeeded

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| success\_date | date    |
+--------------+---------+
Primary key for this table is success\_date.
Succeeded table contains the days of succeeded tasks.

A system is running one task every day. Every task is independent of the previous tasks. The tasks can fail or succeed.

Write an SQL query to generate a report of period_state for each continuous interval of days in the period from 2019-01-01 to 2019-12-31.

period_state is *'failed'*if tasks in this interval failed or 'succeeded' if tasks in this interval succeeded. Interval of days are retrieved as start_date and end_date.

Order result by start_date.

The query result format is in the following example:

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        |
+-------------------+

Result table:
+--------------+--------------+--------------+
| 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   |
+--------------+--------------+--------------+
The report ignored the system state in 2018 as we care about the system in the period 2019-01-01 to 2019-12-31.
From 2019-01-01 to 2019-01-03 all tasks succeeded and the system state was "succeeded".
From 2019-01-04 to 2019-01-05 all tasks failed and system state was "failed".
From 2019-01-06 to 2019-01-06 all tasks succeeded and system state was "succeeded".

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