如何从表中的两行中删除 NULL 值

Question

我得到的输出是这个。

2015-10-01 NULL
NULL NULL
NULL NULL
NULL 2015-10-05
2015-10-11 NULL
NULL 2015-10-13
2015-10-15 2015-10-16
2015-10-25 NULL
NULL NULL
NULL NULL
NULL NULL
NULL NULL
NULL 2015-10-31

我想要这个

2015-10-01  2015-10-05
2015-10-11  2015-10-13
2015-10-15  2015-10-16
2015-10-25  2015-10-31 

我的代码：

select (case when (end_lag <> start_date) or end_lag is null then start_date end) as start_date, 
       (case when (start_lead <> end_date) or start_lead is null then end_date end) as end_date
from
    (select lead(start_date) over(order by start_date) as start_lead, start_date, end_date,                     lag(end_date) over(order by end_date) as end_lag
    from projects) t1;

原始表有两个属性（start_date，end_date），我为start_date创建了lead列，为end_date创建了lag列

Answer 1

从当前的结果表中可以看到：

select start_date, end_date
from (select row_number() over(order by null) rn, start_date
      from current_t
      where start_date is not null) a
join (select row_number() over(order by null) rn, end_date
      from current_t
      where end_date is not null) b
on b.rn = a.rn;

(sql 小提琴here)

Answer 2

您的行似乎没有排序。因此，您可以取消旋转并将它们配对：

select min(dte), nullif(max(dte), min(dte))
from (select x.dte, row_number() over (order by dte) as seqnum
      from projects p cross join lateral
           (select p.start_date as dte from dual union all
            select p.end_date from dual
           ) x
     ) p
group by ceil(seqnum / 2)

Answer 3

忽略两个 NULL 并从原始查询中获取前导值。我想它可以被简化，如果没有 DDL 和样本数据就很难知道。

select *
from (
   select start_date, 
          case when end_date is null then lead(end_date) over(order by coalesce(start_date, end_date)) else end_date end end_date
   from (
      select * 
      from (
           -- your original query
           select (case when (end_lag <> start_date) or end_lag is null then start_date end) as start_date, 
                 (case when (start_lead <> end_date) or start_lead is null then end_date end) as end_date
           from (
             select lead(start_date) over(order by start_date) as start_lead, start_date, end_date,                     
             lag(end_date) over(order by end_date) as end_lag
             from projects) t1
          ---
     ) tbl
     where not (start_date is null and end_date is null )
   ) t
) t
where start_date is not null
order by start_date;