Question

Below is what I have

+++++++++++++++++
+id1    +   id2 +
+++++++++++++++++
+  1    +    2  +
+  2    +    1  +
+  1    +    3  +
+  3    +    2  +
+  4    +    5  +
+  5    +    4  +
+++++++++++++++++

What I want to find is the id of two person which are in both column.

Below is what I will have

+++++++++++++++++
+id1    +   id2 +
+++++++++++++++++
+  1    +    2  +
+  2    +    1  +
+  4    +    5  +
+  5    +    4  +
+++++++++++++++++

OR

+++++++++++++++++
+id1    +   id2 +
+++++++++++++++++
+  1    +    2  +
+  4    +    5  +
+++++++++++++++++

OR

+++++++++++++++++
+id1    +   id2 +
+++++++++++++++++
+  2    +    1  +
+  5    +    4  +
+++++++++++++++++

Any idea how to achieve this?

Here is testing data

Answer 1

This should get you started:

SELECT
    mytable1.id1, mytable1.id2
FROM
    myTable mytable1,
    myTable mytable2
WHERE
    mytable1.id1 = mytable2.id2
    AND
    mytable2.id1 = mytable1.id2
ORDER BY
    mytable1.id1

Demo