如何选择每行sql中存在的值

Question

我需要检查表“List”的每一行的“nS”列的值是否相同，然后显示该值。

Example01 ：这应该返回“S1”，因为每一行在“nS”列中都有该值。

|  nS  |  nE  |
|:-----|-----:|
| 'S1' | 'A1' |
| 'S1' | 'A2' |
| 'S1' | 'A3' |
| 'S1' | 'A4' |

Example02 ：这不应返回任何内容，因为 'nS' 的值不同。

|  nS  |  nE  |
|:-----|-----:|
| 'S1' | 'A1' |
| 'S2' | 'A2' |
| 'S1' | 'A3' |
| 'S3' | 'A4' |

到目前为止，我做了下面的代码，但它不起作用，因为 GROUP BY 语句。

SELECT nS FROM List GROUP BY nS HAVING count(nS) = count(*);

Answer 1

像这样的东西？

SQL> with test (ns, ne) as
  2    (select 's1', 'a1' from dual union all
  3     select 's1', 'a2' from dual union all
  4     select 's1', 'a3' from dual union all
  5     select 's1', 'a4' from dual
  6    )
  7  select distinct ns
  8  from test
  9  where 1 = (select count(distinct ns) From test);

NS
--
s1

SQL>
SQL> with test (ns, ne) as
  2    (select 's1', 'a1' from dual union all
  3     select 's2', 'a2' from dual union all
  4     select 's1', 'a3' from dual union all
  5     select 's3', 'a4' from dual
  6    )
  7  select ns
  8  from test
  9  where 1 = (select count(distinct ns) From test);

no rows selected

SQL>

Answer 2

在您的查询中，您必须将COUNT(*)替换为返回表中总行数的子查询：

SELECT nS
FROM List
GROUP BY nS
HAVING COUNT(*) = (SELECT COUNT(*) FROM List);