一、ascii函数只取给予参数中第一位的asc值

SQL> select ascii('nihao') from dual;

ASCII('NIHAO')
--------------
110

SQL> select ascii('n') from dual;

ASCII('N')
----------
110

二、substr是按字节取字符

SQL> select substr('guojun',1,1) from dual;

S
-
g

SQL> select substr('guojun',1,2) from dual;

SU
--
gu

SQL> select substr('郭军哈',1,1) from dual;

S
-
?

SQL> select substr('郭军哈',1,2) from dual;

SU
--
郭
--因为英文占两个字节，中文占四个字节