foo.sql

mysql> create temporary table tmp (d INT(11));
Query OK, 0 rows affected (0.02 sec)

/* there are 2 rows being inserted with value of 1 */
mysql> insert into tmp (d) values (1), (2), (1), (3);
Query OK, 4 rows affected (0.01 sec)

/* this shows that distinct works */
mysql> select distinct d from tmp;
+------+
| d    |
+------+
|    1 |
|    2 |
|    3 |
+------+
3 rows in set (0.00 sec)

/* This shows that if a row becomes different then distinct operates off the row */
mysql> select distinct d, RAND() as e from tmp;
+------+---------------------+
| d    | e                   |
+------+---------------------+
|    1 |  0.8762416912952826 |
|    2 | 0.09092339043591487 |
|    1 |  0.8258919090273714 |
|    3 |  0.8566894045627578 |
+------+---------------------+
4 rows in set (0.01 sec)