Sprawdziłem na trzech różnych serwerach i u mnie wynik jest jak najbardziej prawidłowy:
Kod
mysql> SELECT VERSION();
+------------+
| VERSION() |
+------------+
| 4.1.12a-nt |
+------------+
1 row in set (0.03 sec)
mysql> SELECT LOWER('ASDFasdfASDF');
+-----------------------+
| LOWER('ASDFasdfASDF') |
+-----------------------+
| asdfasdfasdf |
+-----------------------+
1 row in set (0.02 sec)
Kod
mysql> SELECT VERSION();
+-----------------+
| VERSION() |
+-----------------+
| 4.1.11-standard |
+-----------------+
1 row in set (0.01 sec)
mysql> SELECT LOWER('ASDFasdfASDF');
+-----------------------+
| LOWER('ASDFasdfASDF') |
+-----------------------+
| asdfasdfasdf |
+-----------------------+
1 row in set (0.00 sec)
Kod
mysql> SELECT VERSION();
+-----------------+
| VERSION() |
+-----------------+
| 4.0.25-standard |
+-----------------+
1 row in set (0.05 sec)
mysql> SELECT LOWER('ASDFasdfASDF');
+-----------------------+
| LOWER('ASDFasdfASDF') |
+-----------------------+
| asdfasdfasdf |
+-----------------------+
1 row in set (0.03 sec)
Sprawdź dokładnie jaką masz wersję MySQL'a, poszukaj może gdzieś masz błędy.