Get distinct records from 2 union sql statement - mysql

Question

I would like to seek the advice of some sql experts.
I wrote sql statement for getting authors names from staff and alumni table. Some author's name will be in both tables. So the logic is if the author name is in staff, use that otherwise look for alumni table.
Here is my sql statement, seems fine but it is showing same author name from both staff and alumni table.
SELECT DISTINCT AP.Author_name, P.people_id, P.Name, P.Journal_name, AP.Author_sortorder FROM `Paper_Author` AS AP LEFT JOIN `People` AS P ON ( AP.Author_id = P.people_id ) WHERE AP.Paper_id =3838
UNION
SELECT DISTINCT AN.Author_name, N.People_id, N.Name, N.Journal_name, AN.Author_sortorder FROM `Paper_Author` AS AN LEFT JOIN `Alumni` AS N ON ( AN.Author_id = N.People_id ) WHERE AN.Paper_id =3838 ORDER BY Author_sortorder LIMIT 0 , 30
Result:
people_id-- Author_name-- Journal_name--
1 Name1 A1
2 Name2 B1
3 Name3 C1
3 Name3 C1
4 Name4 D
4 Name4
Expected Result :
people_id-- Author_name-- Journal_name--
1 Name1 A1
2 Name2 B1
3 Name3 C1
4 Name4 D

Answer 1

This can probably be solved by an additional select using the original result as a subquery
SELECT DISTINCT * FROM (
SELECT DISTINCT AP.Author_name, P.people_id, P.Name, P.Journal_name, AP.Author_sortorder FROM `Paper_Author` AS AP LEFT JOIN `People` AS P ON ( AP.Author_id = P.people_id ) WHERE AP.Paper_id =3838
UNION
SELECT DISTINCT AN.Author_name, N.People_id, N.Name, N.Journal_name, AN.Author_sortorder FROM `Paper_Author` AS AN LEFT JOIN `Alumni` AS N ON ( AN.Author_id = N.People_id ) WHERE AN.Paper_id =3838 ORDER BY Author_sortorder LIMIT 0 , 30
);

Answer 2

The difficulty with this problem is that you might need information from either the People or Alumni tables. We would like to just join to a single table containing the right information. Much of the complexity of the below query is in creating a table which contains the right metadata for each person.
SELECT
pa.Author_name,
pa.Author_sortorder,
t1.people_id,
t1.Name,
t1.Journal_name
FROM Paper_Author pa
LEFT JOIN
(
SELECT people_id, Name, Journal_name, 0 AS source
FROM People
UNION ALL
SELECT people_id, Name, Journal_name, 1
FROM Alumni
) t1
ON pa.Author_id = t1.people_id
INNER JOIN
(
SELECT people_id, MIN(source) AS source
FROM
(
SELECT people_id, 0 AS source
FROM People
UNION ALL
SELECT people_id, 1
FROM Alumni
) t
GROUP BY people_id
) t2
ON t1.people_id = t2.people_id AND
t1.source = t2.source
WHERE
pa.Paper_id = 3838;