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Taking count from pair values ​​in a table

count_temp table

take the above as the output of the sample table, I need a sql query that results in "2" as the amount from the table.

I tried to do this while the column sent to 4, and everything was fine; but the other lines display the wrong o / p value. my old code is specified

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 )
     ) ;

Thanks in advance and thanks.

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2 answers

Your request:

with cte as (
select distinct m1.sentby , m1.sentto
from m m1 
inner join m m2
   on m1.sentby = m2.sentto and
      m2.sentby = m1.sentto 
)
select count(*)/2 from cte;

check it on sqlfiddle

Also, simplifying:

select count( distinct m1.sentby ) / 2
from m m1 
inner join m m2
   on m1.sentby = m2.sentto and
      m2.sentby = m1.sentto
+1
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Try the following:

    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;
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