SQL選擇唯一行

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。 我正在嘗試編寫一個查詢，該查詢僅在只有一個唯一的CURRENT記錄且IDENT = CURRENT（示例2）的記錄上顯示*。 有些記錄具有相同的CURRENT但具有不同的IDENT（示例1），這些記錄應從結果中省略。

我正在嘗試在IDENT = CURRENT的所有當前查詢中顯示與示例1類似的結果。不確定是否需要使用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)

或沒有子查詢

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