sql - 从表中的对值中获取计数

Question

将以上内容作为样本表的输出，
我需要一个 sql 查询，它的结果是“2”作为表中的计数。

我已经尝试过，直到第 4 列发送时，还可以；
但更多行显示不正确的 o/p。给出了我的旧代码

SELECT COUNT(*)/2
     FROM 
     (SELECT sentby,sentto
     FROM
          (SELECT DISTINCT sentby, sentto FROM count_temp)
     WHERE sentto IN
          (SELECT DISTINCT sentby FROM count_temp )
      AND sentby IN
          (SELECT DISTINCT sentto FROM count_temp )
     ) ;

提前致谢:) 并表示赞赏。

Answer 1

试试这个:

    SELECT count(*)/2
    FROM
      (SELECT sentby,
              sentto,
              max(rownum) AS rn
       FROM count_temp
       GROUP BY sentby,
                sentto) a,
      (SELECT sentby,
              sentto,
              max(rownum) AS rn
       FROM count_temp
       GROUP BY sentby,
                sentto) b
    WHERE a.rn != b.rn
      AND a.sentby = b.sentto
      AND a.sentto = b.sentby;