length是字的长度，lengthb是字节的长度，字符集为UTF8

SQL> create table test(a varchar2(20));

Table created

SQL> insert into test values('2');

1 row inserted

SQL> insert into test values('12');

1 row inserted

SQL> insert into test values('四大皆空');

1 row inserted

SQL> commit;

Commit complete

SQL> select * from test;

A
--------------------
2
12
四大皆空

SQL> select a from test where length(a)!=lengthb(a);

A
--------------------
四大皆空

SQL> select a from test where asciistr(a) not like '%%';

A
--------------------
2
12

SQL> select a from test where asciistr(a) like '%%';

A
--------------------
四大皆空

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判断字段中是否含有中文字符