入住另一列（NULL或NOT NULL）和所有的值返回唯一記錄

Question

正如你看到的CID = 1所有日期字段都爲NULL和CID = 3的所有日期字段不爲空。

如果所有日期都爲NULL，那麼使用「NULL」，如果所有日期都不是NULL，那麼使用「NOT NULL」，我需要使用新字段獲得唯一的cids。

cid - new field 
1 - NULL 
3 - NOT NULL 

Answer 1

您可以通過聚集和case做到這一點：

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)