SQL选择唯一行

Question

范例1：

IDENT | CURRENT | SOURCE
12345 | 12345   | A
23456 | 12345   | B
34567 | 12345   | C

范例2：

IDENT | CURRENT | SOURCE
56789 | 56789   | A 

具有3列的表，IDENT，CURRENT和SOURCE。 我正在尝试编写一个查询，该查询仅在只有一个唯一的CURRENT记录且IDENT = CURRENT（示例2）的记录上显示*。 有些记录具有相同的CURRENT但具有不同的IDENT（示例1），这些记录应从结果中省略。

我正在尝试在IDENT = CURRENT的所有当前查询中显示与示例1类似的结果。不确定是否需要使用WHERE CURRENT COUNT = 1。

Answer 1

select * from table 
where ident=current 
and current in (select current from table group by 1 having count(*)=1)

或没有子查询

select 
min(ident) as ident, 
current, min(source) as source
from table 

where ident=current 
group by current
having count(*)=1

Answer 2

SELECT M.* 
FROM Table1 AS M 
WHERE M.IDENT = M.CURRENT 
AND (
      SELECT COUNT(*) 
      FROM Table1 AS S 
      WHERE M.IDENT = S.IDENT 
      AND M.CURRENT = S.CURRENT
    ) = 1