MySQL query to find partial duplicates

Question

I have a table in which I would like to seek out contestants who wrote more than one contest. There are more columns but the only ones I'm looking at are first_name, last_name, school, and contest.

I want to find people in my table who wrote more than one contest, so basically same first_name, same last_name, same school, BUT different contest. There are 3 possible contests.

Also, each contestant has a contestant_id which is the primary key.

EDIT

I should have specified that contest must equal 1 of the 3 contests I specify. The table could have contestants from other contests I'm not looking at and it would be beneficial to list even the duplicates. So if it finds 2 people matching the criteria, it shows both.

EDIT 2

Some example data…

| id | first_name | last_name | school | contest |  
| 01 |   Jane     |    Doe    |  2568  |   1001  |  
| 02 |   Mike     |    Doe    |  2568  |   1003  |  
| 03 |   Jane     |    Doe    |  2568  |   1003  |  
| 04 |   Jane     |    Doe    |  2523  |   1001  |  

In this example id 01 and 03 would match but the others would not because the name is different with 02 and school is different with 04.

Answer 1

SELECT  first_name,last_name,school,contest FROM table 
WHERE contest IN ('blah','mah','wah')
GROUP BY  first_name, last_name, school 
HAVING COUNT(DISTINCT contest)>1

Edit

SELECT * FROM table t JOIN
(SELECT  GROUP_CONCAT(id)as ids,first_name,last_name,school,contest FROM table
WHERE contest IN (1001,1002,1003)
GROUP BY  first_name, last_name, school 
HAVING COUNT(DISTINCT contest)>1)x
ON FIND_IN_SET(t.id,x.ids)>0

FIDDLE