MYSQL ORDER BY CASE Issue

Question

I have a database like this:

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|   id_one   |   id_two   |   timestamp_one   |   timestamp_         


        

Answer 1

SELECT id_one, id_two, timestamp_one, timestamp_two      
FROM tablename 
WHERE id_one = 27 
    OR id_two = 27 
ORDER BY 
    CASE 
        WHEN id_one=27 THEN timestamp_one 
        WHEN id_two=27 THEN timestamp_two 
    END DESC 

Answer 2

SELECT * FROM tablename 
WHERE id_one=27 OR id_two=27 
ORDER BY id ASC, timestamp_one DESC

Answer 3

SELECT 
   id_one,
   id_two,
   (CASE 
      WHEN id_one=27 THEN timestamp_one
      WHEN id_two=27 THEN timestamp_two    
   END) as timestamp
FROM tablename
ORDER BY timestamp DESC