LeetCode（数据库）- 寻找没有被执行的任务对

题目链接：​​点击打开链接​​

题目大意：略。

解题思路：略。

AC 代码

-- 解决方案(1)
with recursive t(task_id, subtask_id) as (
    SELECT task_id, subtasks_count FROM Tasks
    UNION ALL
    SELECT task_id, subtask_id-1 FROM t where subtask_id-1>0
)

SELECT * FROM t left join Executed using(task_id, subtask_id) 
WHERE Executed.subtask_id is null 
ORDER BY task_id, subtask_id

-- 解决方案(2)
WITH RECURSIVE t AS(
    SELECT 1 num
    UNION ALL
    SELECT num + 1 FROM t WHERE num < (SELECT MAX(subtasks_count) maxn FROM Tasks)
)

SELECT task_id, num subtask_id
FROM Tasks JOIN t
WHERE subtasks_count >= num AND (task_id, num) NOT IN (SELECT * FROM Executed)
ORDER BY task_id, num