If count is less than 1, returns an empty string.
Returns NULL if str or count are NULL.
mysql> SELECT REPEAT('java2s.com ', 3);
+-----------------------------------+
| REPEAT('java2s.com ', 3) |
+-----------------------------------+
| java2s.com java2s.com java2s.com |
+-----------------------------------+
1 row in set (0.00 sec)
mysql>