10g的sqlplus区分大小写问题

sqlplus据说是不区分大小写的，但是我做了个实验感觉还是区分大小写啊?

1)大写
SQL> select count(*) from tab where tname like '%BIN%';

    COUNT(*)
----------
             370

Elapsed: 00:00:00.07
SQL>
2）小写
SQL> select count(*) from tab where tname like '%bin%';

    COUNT(*)
----------
                 0

Elapsed: 00:00:00.06
SQL>

问题：为什么？

doudou@TEST> select * from user_tables where table_name='doudou_test2';

no rows selected
doudou@TEST> select count(*) from    user_tables where table_name='DOUDOU_TEST2';

    COUNT(*)
----------
                 1
doudou@TEST> select count(*) from doudou_test2 where name like 'doudou+小写';

    COUNT(*)
----------
                 1

Elapsed: 00:00:00.00
doudou@TEST> select count(*) from doudou_test2 where name like 'DOUDOU+小写';

    COUNT(*)
----------
                 0

Elapsed: 00:00:00.00
doudou@TEST> select * from doudou_test2;

ID                                                                             NAME
---------------------------------------- ----------------------------------------
1                                                                                doudou+小写
2                                                                                DOUDOU+大写

Elapsed: 00:00:00.01