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
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