select substring_index('AAAA.BCCC','.',1)
union all
select reverse(substring_index(reverse('AAAA.BCCC'),'.',1))
结果
+------------------------------------+
| substring_index('AAAA.BCCC','.',1) |
+------------------------------------+
| AAAA |
| BCCC |
+------------------------------------+
2 rows in set (0.00 sec)