Question

我正在绞尽脑汁试图找出哪个群体和/或不同的count()形成帮助，但目前已经空白了。

考虑一下表：

PersonId | PlaceName
---------+----------
    1    |   NULL
    1    |   NULL
    2    |   NULL
    2    | Las Vegas
    3    | London
    4    |   NULL
    4    |   NULL
    4    |   NULL

我正在寻找那些没有费心填写“地名”的人，所以我希望我的输出看起来像这样：

PersonId
--------
    1
    4

我实际上会加入其他一些表来提取每个“捣蛋”人的信息，但问题的关键在于上面的问题。

Answer 1

使用以下查询：

SELECT PersonId
  FROM TheTable
 GROUP BY PersonId
 HAVING COUNT(PlaceName) = 0

COUNT()聚合函数会忽略NULL，因此应返回正确的结果。

Answer 2

select PersonId
from MyTable
group by PersonId
having count(case when PlaceName is not null then 1 end) = 0

SQL Fiddle Example

Answer 3

select distinct t1.id
from test t1
LEFT JOIN
(
  select id, count(name) nm
  from test 
  where name is not null
  group by id
) x
  on t1.id = x.id
where x.nm is null

请参阅SQL Fiddle with Demo

Answer 4

我会提供以下内容：

select distinct a.personid 
  from tablename a
  left outer join tablename b
    on a.personid=b.personid
   and b.placename is not null
 where b.personid is null
order by personid

Answer 5

SELECT DISTINCT PersonId
FROM MyTable t
WHERE NOT EXISTS(SELECT 1 FROM MyTable WHERE PersonId = t.PersonId AND PlaceName is not null)

SQL查找哪些成员只有空条目

5 个答案: