How to avoid duplicate entries with SELECT statement? +----+----------------------+---------+---------+---------------------+-------+
| id | translation          | id_word | id_user | added               | tuser |
+----+----------------------+---------+---------+---------------------+-------+
| 17 | допомагати           |       4 |       1 | 2013-08-29 14:52:20 |     2 |
| 17 | допомагати           |       4 |       1 | 2013-08-29 14:52:20 |     1 |
|  5 | когось               |       1 |       1 | 2013-08-27 23:35:09 |     1 |
|  4 | хто-небудь           |       1 |       1 | 2013-08-27 23:35:09 |  NULL |
|  1 | хтось                |       1 |       1 | 2013-08-27 23:34:17 |     2 |
|  1 | хтось                |       1 |       1 | 2013-08-27 23:34:17 |     1 |
+----+----------------------+---------+---------+---------------------+-------+


As you can see, I have duplicate entries in id. I have to avoid duplicate entries if: 

There is a row with a tuser = 1, then I have to remove other entries with the same id, id_user and id_word from result.
If in rows (with id, id_user and id_word) no tuser = 1, it must show all values.

I need only one unique row if tuser  = 1 for each unique combination id, id_word, id_user
SELECT a.*                                -- select all rows
FROM tableX  a                            -- from table
WHERE a.tuser = 1                         -- where either tuser = 1
   OR NOT EXISTS                          -- or there is no other 
      ( SELECT *                          -- row 
        FROM tableX  b                    -- in the table
        WHERE b.tuser = 1                 -- with tuser = 1
          AND b.id = a.id                 -- and same "id",
          AND b.id_user = a.id_user       -- same "id_user"
          AND b.id_word = a.id_word       -- and same "id_word"
      ) ;