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".