If count is positive, everything to the left of the final delimiter is returned.
If count is negative, everything to the right of the final delimiter is returned.
SUBSTRING_INDEX() performs a case-sensitive match when searching for delim.
mysql>
mysql> SELECT SUBSTRING_INDEX('www.rntsoft.com', '.', 2);
+-------------------------------------------+
| SUBSTRING_INDEX('www.rntsoft.com', '.', 2) |
+-------------------------------------------+
| www.rntsoft |
+-------------------------------------------+
1 row in set (0.00 sec)
mysql>