一、原题描述
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".
二、简要翻译
两张表，Failed 和 Succeeded，用来记录一个每日定时跑的系统任务的失败和成功。要求返回一张结果表，按顺序展示该任务失败和成功的连续时间段以及起止时间。
三、SQL分析
1、将两张表里面的数据按照时间是否连续进行分组。
1 #失败表 2 SELECT 3 fail_date, 4 IF( 5 @date = DATE_SUB(fail_date, INTERVAL 1 DAY), 6 @rank := @rank, 7 @rank := @rank + 1 8 ) AS rank, 9 @date := fail_date 10 FROM 11 Failed, 12 (SELECT 13 @date := NULL, 14 @rank := 0) r 15 WHERE fail_date > '2018-12-31' 16 AND fail_date < '2020-01-01' 17 ORDER BY fail_date； 18 19 #成功表 20 SELECT 21 success_date, 22 IF( 23 @date = DATE_SUB(success_date, INTERVAL 1 DAY), 24 @rank := @rank, 25 @rank := @rank + 1 26 ) AS rank, 27 @date := success_date 28 FROM 29 Succeeded, 30 (SELECT 31 @date := NULL, 32 @rank := 0) r 33 WHERE success_date > '2018-12-31' 34 AND success_date < '2020-01-01' 35 ORDER BY success_date
2、将上一步的两张表分组查询最大日期，最小日期，然后合并再排序
1 SELECT 2 * 3 FROM 4 (SELECT 5 'succeeded' AS period_state, 6 MIN(success_date) AS start_date, 7 MAX(success_date) AS end_date 8 FROM 9 (SELECT 10 success_date, 11 IF( 12 @date = DATE_SUB(success_date, INTERVAL 1 DAY), 13 @rank := @rank, 14 @rank := @rank + 1 15 ) AS rank, 16 @date := success_date 17 FROM 18 Succeeded, 19 (SELECT 20 @date := NULL, 21 @rank := 0) r 22 WHERE success_date > '2018-12-31' 23 AND success_date < '2020-01-01' 24 ORDER BY success_date) t1 25 GROUP BY t1.rank 26 UNION 27 ALL 28 SELECT 29 'failed' AS period_state, 30 MIN(fail_date) AS start_date, 31 MAX(fail_date) AS end_date 32 FROM 33 (SELECT 34 fail_date, 35 IF( 36 @date = DATE_SUB(fail_date, INTERVAL 1 DAY), 37 @rank := @rank, 38 @rank := @rank + 1 39 ) AS rank, 40 @date := fail_date 41 FROM 42 Failed, 43 (SELECT 44 @date := NULL, 45 @rank := 0) r 46 WHERE fail_date > '2018-12-31' 47 AND fail_date < '2020-01-01' 48 ORDER BY fail_date) t2 49 GROUP BY t2.rank) temp 50 ORDER BY start_date ;