SQL> select substr('aaa_100kg_5',instr('aaa_100kg_5','_',1,2)+1) from dual;S
-
5SQL> select substr('bbcc_2kg_399',instr('bbcc_2kg_399','_',1,2)+1) from dual;SUB
---
399
-
5SQL> select substr('bbcc_2kg_399',instr('bbcc_2kg_399','_',1,2)+1) from dual;SUB
---
399
select substr(aa,instr(aa,'_',Instr(aa, '_')+1)+1) from table t