how do i combine 2 rows appending a column from the second row in the final result?

Question

I asked this question before but still have not been able to get this working. Someone suggested a self join but I don't see where that will work. I am still getting 2 rows with the incorrect results. The self join is still present but I just can't seem to get the results I need.

I want to go from this:

id   sender          recipient
1   Administrator Administrator
1   Miller         Miller

To this:

id   sender          recipient
1   Administrator Miller

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Here is the SQL that I am working with.

SELECT
t1.msg_id AS id,
t3.lastname AS sender,
t4.lastname AS recipient
FROM
mail_message AS t1
Inner Join mailbox AS t2 ON t2.msg_id = t1.msg_id
Inner Join employee AS t3 ON t3.employee_id = t2.employee_id
Inner Join employee AS t4 ON t3.employee_id = t4.employee_id

Answer 1

Your last join (t3.employee_id = t4.employee_id) is clearly wrong - you're joining employee on itself. You need to replace that condition with join on either mailbox or mail_message - it's hard to say without seeing your exact table structure. Can you post it?