检查另一列中的所有值（NULL或NOT NULL）并返回唯一记录

Question

如您所见，对于cid = 1，所有日期字段均为NULL，而对于cid = 3，所有日期字段均为NOT NULL。

我需要使用新字段获取唯一的cid，如果所有日期都为NULL，则为“NULL”，如果所有日期都为NOT NULL，则为“NOT NULL”。

cid - new field
1 - NULL
3 - NOT NULL

Answer 1

您可以使用聚合和case：

执行此操作

select cid,
       (case when count(datecol) = 0 then 'NULL'
             when count(datecol) = count(*) then 'NOT NULL'
        end) as newField
from t
group by cid
having count(datecol) in (0, count(*));

Answer 2

select cid, case when min(c) = 0 AND max(c) = 0 then 'null' when min(c) = 1 and max(c) = 1 then 'not null' end from (
    select cid, case when dt is null then 0 else 1 end as c from your_table
) t
group by cid
having min(c) = max(c)