REPLACE() performs a case-sensitive match when searching for from_str.
mysql>
mysql> SELECT REPLACE('www.rntsoft.com', 'w', 'W');
+-------------------------------------+
| REPLACE('www.rntsoft.com', 'w', 'W') |
+-------------------------------------+
| WWW.rntsoft.com |
+-------------------------------------+
1 row in set (0.00 sec)
mysql>