sql - 从其他范围中找到最大范围

Question

我有一个表描述为

create table range (
    x int not null,
    y int not null,
    check (x < y)
);

表格充满了这样的范围

insert into range(x,y) values (1,5);
insert into range(x,y) values (2,6);
insert into range(x,y) values (2,3);
insert into range(x,y) values (4,6);
insert into range(x,y) values (2,6);

insert into range(x,y) values (9,10);
insert into range(x,y) values (8,11);
insert into range(x,y) values (7,9);

insert into range(x,y) values (12,15);

我想用一些选择查询表，它返回最大连续范围。

select ????? from range
x , y
--------------
1 , 6
7 , 11
12, 15 

我需要递归或窗口函数吗？

Answer 1

这是一个差距和孤岛问题。这个想法是找到每个组的开始位置，然后使用累积和来定义组(“岛”)。然后聚合:

select min(x) as x, max(y) as y
from (select r.*,
            sum(isstart) over (order by x range between unbounded preceding and current row) as grp
      from (select r.*,
                   (not exists (select 1
                                from range r2
                                where r2.x < r.x and r2.y >= r.x
                               )
                   )::int as isstart
            from range r
           ) r
     ) r
group by grp
order by min(x);

Here是一个 SQL fiddle 。

注意:range between 应该处理多个范围从同一日期开始并开始一个感兴趣的时间段的情况。