如何在一列中获取四个连续的空值

Question

有：

create table theater(seatno varchar2(3),status varchar(1));

insert into theater('A1','');
insert into theater('A2','B');
insert into theater('A3','B');
insert into theater('A4','');
insert into theater('A5','');
insert into theater('A6','');
insert into theater('A7','');

我的要求是获取状态为空的四个连续座位号
A4,A5,A6,A7

我尝试了Lead，Lag功能，但没有成功。

Answer 1

第一步，状态为空（琐碎）：

select * from  theater
where status is null

现在我们将座位分成连续的组：

select seat - row_number() over (order by seat) grp, seat
where status is null

这样可以为连续座位提供相同的座位

grp   seat
---   ----
0     1
0     2
1     4
1     5

然后在小组中要求下一个第四要素

select lead(seat, 4) over (partition by grp), grp, seat from (
previous query
)

最后，您要过滤第4个元素不为null。 那就是你的答案。

Answer 2

这样的事情应该有所帮助。

select t1.seatno
, t2.seatno
, t3.seatno
, t4.seatno

from theatre t1 join theatre t2 on t2.seatno = t1.seatno + 1
join theatre t3 on t3.seatno = t2.seatno + 1
join theatre t4 on t4.seatno = t3.seatno + 1

where t1.status is null
and t2.status is null
and t3.status is null
and t4.status is null

Answer 3

我将使用派生表添加row_seatno和col_seatno列，然后使用listagg函数创建整个行状态的聚合列表。

接下来，我将连续找到4个NULL的实例，它们的子字符串为'N; N; N; N'，如下所示：

        select seatno
  ||', '
  || mod3_t.row_seatno
  || to_char( to_number(mod3_t.col_seatno) + 1)
  || ', '
  || mod3_t.row_seatno
  || to_char( to_number(mod3_t.col_seatno) + 2)
  || ', '
  || mod3_t.row_seatno
  || to_char(to_number(mod3_t.col_seatno) + 3)
from
  (select mod2_t.seatno,
    mod2_t.row_seatno,
    mod2_t.col_seatno,
    instr(mod2_t.row_status, 'N;N;N;N', to_number(mod2_t.col_seatno) ,1) cont_null
  from
    (select mod1_t.seatno,
      mod1_t.row_seatno,
      mod1_t.col_seatno,
      listagg(nvl(mod1_t.status,'N'), ';') within group (
    order by mod1_t.col_seatno) over (partition by mod1_t.row_seatno ) row_status
    from
      (select regexp_substr( t.seatno, '[[:upper:]]+',1,1) row_seatno,
        regexp_substr( t.seatno, '[[:digit:]]+',1,1) col_seatno,
        seatno,
        status
      from theater t
      ) mod1_t
    ) mod2_t
  where cont_null =1
  ) mod3_t