oracle中gbk和utf8的数据库在默认nls_comp、nl_sort默认都是binary，对大小写敏感。
数据库是GBK的情况
当设置nls_somp = LINGUISTIC or ANSI 且 nls_sort= binary_ci的情况大小写不敏感，其他均大小写敏感。
数据库为UTF8的是情况
当设置nls_somp = LINGUISTIC or ANSI 且nls_sort= languagename_ci的情况大小写不敏感，nls_sort= languagname的时候大小写敏感。
===========================================================
select * from nls_database_parameters where parameter='NLS_CHARACTERSET';
select * from NLS_SESSION_PARAMETERS where parameter in ('NLS_COMP','NLS_SORT');
select * from NLS_DATABASE_PARAMETERS where parameter in ('NLS_COMP','NLS_SORT');
select * from NLS_Instance_Parameters where parameter in ('NLS_COMP','NLS_SORT');
ALTER SESSION SET NLS_COMP=LINGUISTIC;
ALTER SESSION SET NLS_SORT=BINARY_CI;
create table cw(name varchar2(20));
insert into cw values('IPTV');
insert into cw values('iptv');
insert into cw values('Iptv');
select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw;
select SYS_CONTEXT('USERENV','CURRENT_SCHEMA') CURRENT_SCHEMA from dual
============================================================================
nls_comp
nls_comp的值影响sql的比较行为。
oracle允许在各个字符集上进行基于语言的比较，排序操作，正常做法是通过系统函数实现，比较麻烦，可以通过设置nls_comp为LINGUISTIC，再结合nls_sort简化。
nls_comp 默认是BINARY，允许范围：BINARY , LINGUISTIC, or ANSI
当设置LINGUISTIC时需要设置NLS_SORT才能生效，ANSI就是LINGUISTIC的兼容参数，正常应该使用LINGUISTIC。
可以通过ALTER SESSION SET NLS_COMP = LINGUISTIC; 设置
一旦把nls_comp设置为LINGUISTIC需要根据nls_sort这是的情况重新创建索引，否则会照成索引失效。
CREATE INDEX i ON t(NLSSORT(col, 'NLS_SORT=FRENCH'));
The value of NLS_COMP affects the comparison behavior of SQL operations.
You can use NLS_COMP to avoid the cumbersome process of using the NLSSORT function in SQL statements when you want to perform a linguistic comparison instead of a binary comparison. When NLS_COMP is set to LINGUISTIC, SQL operations perform a linguistic comparison based on the value of NLS_SORT. A setting of ANSI is for backward compatibility; in general, you should set NLS_COMP to LINGUISTIC when you want to perform a linguistic comparison.
nls_sort
The NLS_SORT option specifies the sequence of character values used when sorting or comparing text. The value of NLS_SORT affects the GT,GE, LT, and LE operators, SORT command, and the SORTLINES function.
Within a session, you can dynamically modify the value of this option using the OLAP DML syntax show below or by using the SQL statementALTER SESSION SET option = value.
nls_sort选项指明在所文本排序或者比较的时候character的值得顺序，它会影响到gt，ge，lt and le 操作，以及sort命令和sortlines 函数。这里没有明确说是否影响等于操作符。
字符集与nls_comp\nls_sort
通过实际验证gbk和utf8的数据库在默认nls_comp、nl_sort默认都是binary，对大小写敏感。
数据库是GBK的情况
当设置nls_somp = LINGUISTIC or ANSI 切 nls_sort= binary_ci的情况大小写不敏感，其他均大小写敏感。
数据库为UTF8的是情况
当设置nls_somp = LINGUISTIC or ANSI 切 nls_sort= languagename_ci的情况大小写不敏感，nls_sort= languagename的时候大小写敏感。
GBK数据库
SQL> conn test/[email protected]:1521/orcl
Connected.
SQL> select * from nls_database_parameters where parameter='NLS_CHARACTERSET';
PARAMETER VALUE
------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_CHARACTERSET ZHS16GBK
SQL> select * from NLS_SESSION_PARAMETERS where parameter in ('NLS_COMP','NLS_SORT');
PARAMETER VALUE
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_SORT BINARY
NLS_COMP BINARY
SQL> ALTER SESSION SET NLS_COMP=LINGUISTIC;
ALTER SESSION SET NLS_SORT=BINARY_CI;
Session altered.
SQL>
Session altered.
SQL> select * from test.cw ;
NAME
------------------------------------------------------------
IPTV
iptv
Iptv
SQL> select * from test.cw where name = 'iptv';
NAME
------------------------------------------------------------
IPTV
iptv
Iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
1
1
1
SQL> ALTER SESSION SET NLS_SORT=BINARY;
Session altered.
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw 2 ;
CASEWHEN
----------
1
2
3
SQL> select * from test.cw where name = 'iptv';
NAME
------------------------------------------------------------
iptv
SQL> ALTER SESSION SET NLS_SORT='XSPANISH';
Session altered.
SQL> select * from test.cw where name = 'iptv';
NAME
------------------------------------------------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw 2 ;
CASEWHEN
----------
1
2
3
SQL> ALTER SESSION SET NLS_SORT='XSPANISH_CI';
Session altered.
SQL> select * from test.cw where name = 'iptv';
NAME
------------------------------------------------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw 2 ;
CASEWHEN
----------
1
2
3
SQL> ALTER SESSION SET NLS_SORT='ITALIAN';
Session altered.
SQL> select * from test.cw where name = 'iptv';
NAME
------------------------------------------------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw 2 ;
CASEWHEN
----------
1
2
3
SQL> ALTER SESSION SET NLS_SORT='ITALIAN_CI';
Session altered.
SQL> select * from test.cw where name = 'iptv';
NAME
------------------------------------------------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw 2 ;
CASEWHEN
----------
1
2
3
SQL>
UTF8数据库
SQL> conn sys/[email protected]:1521/oral2 as sysdba
Connected.
SQL> set line 2000
SQL> select * from nls_database_parameters where parameter='NLS_CHARACTERSET';
PARAMETER VALUE
------------------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_CHARACTERSET AL32UTF8
SQL> select * from NLS_SESSION_PARAMETERS where parameter in ('NLS_COMP','NLS_SORT');
PARAMETER VALUE
------------------------------------------------------------------------------------------------------------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_SORT BINARY
NLS_COMP BINARY
SQL> select * from sys.cw ;
NAME
--------------------
iptv
IPTV
Iptv
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw;
2
CASEWHEN
----------
2
1
3
SQL> ALTER SESSION SET NLS_COMP=LINGUISTIC;
Session altered.
SQL> ALTER SESSION SET NLS_SORT=BINARY_CI;
Session altered.
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
IPTV
Iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
1
1
1
SQL> ALTER SESSION SET NLS_SORT='XSPANISH';
Session altered.
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
2
1
3
SQL> ALTER SESSION SET NLS_SORT='XSPANISH_CI';
Session altered.
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
IPTV
Iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
1
1
1
SQL> ALTER SESSION SET NLS_SORT='ITALIAN';
Session altered.
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
2
1
3
SQL> ALTER SESSION SET NLS_SORT='ITALIAN_CI';
Session altered.
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
IPTV
Iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
1
1
1
SQL> select * from NLS_SESSION_PARAMETERS where parameter in ('NLS_COMP','NLS_SORT');
PARAMETER VALUE
------------------------------------------------------------------------------------------------------------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_SORT ITALIAN_CI
NLS_COMP LINGUISTIC
SQL> ALTER SESSION SET NLS_COMP=BINARY
2 ;
Session altered.
SQL> select * from sys.cw where name = 'iptv';
NAME
--------------------
iptv
SQL> select case when name = 'IPTV' then 1 when name = 'iptv' then 2 when name = 'Iptv' then 3 end casewhen
from cw; 2
CASEWHEN
----------
2
1
3
SQL> select * from NLS_SESSION_PARAMETERS where parameter in ('NLS_COMP','NLS_SORT');
PARAMETER VALUE
------------------------------------------------------------------------------------------------------------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_SORT ITALIAN_CI
NLS_COMP
附录
NLS_SORT
The NLS_SORT option specifies the sequence of character values used when sorting or comparing text. The value of NLS_SORT affects the GT,GE, LT, and LE operators, SORT command, and the SORTLINES function.
Within a session, you can dynamically modify the value of this option using the OLAP DML syntax show below or by using the SQL statementALTER SESSION SET option = value.
Data Type
TEXT
Syntax
NLS_SORT = option-value
Arguments
See Oracle Database Globalization Support Guide for more information about the NLS_SORT parameter.
Examples
Example 6-78 Binary and Linguistic Sorts
A dimension named words has the following values.
cerveza, Colorado, cheremoya, llama, luna, lago
This example shows the results of a binary sort.
NLS_SORT = 'BINARY'
SORT words A words
STATUS words
The current status of WORDS is:
Colorado, cerveza, cheremoya, lago, llama, luna
A Spanish language sort results in this order.
NLS_SORT = 'SPANISH'
SORT words A words
STATUS words
The current status of WORDS is:
cerveza, cheremoya, Colorado, lago, llama, luna
An extended Spanish language sort results in this order.
NLS_SORT = 'XSPANISH'
SORT words A words
STATUS words
The current status of WORDS is:
cerveza TO cheremoya, lago TO llama
Page 128 of 604
NLS_SORT specifies the collating sequence for ORDER BY queries.
- If the value is BINARY, then the collating sequence for ORDER BY queries is based on the numeric value of characters (a binary sort that requires less system overhead).
- If the value is a named linguistic sort, sorting is based on the order of the defined linguistic sort. Most (but not all) languages supported by the NLS_LANGUAGE parameter also support a linguistic sort with the same name.
Note:
Setting NLS_SORT to anything other than BINARY causes a sort to use a full table scan, regardless of the path chosen by the optimizer.BINARY is the exception because indexes are built according to a binary order of keys. Thus the optimizer can use an index to satisfy the ORDER BY clause when NLS_SORT is set to BINARY. If NLS_SORT is set to any linguistic sort, the optimizer must include a full table scan and a full sort in the execution plan.
You must use the NLS_SORT operator with comparison operations if you want the linguistic sort behavior.
The value of NLS_COMP affects the comparison behavior of SQL operations.
You can use NLS_COMP to avoid the cumbersome process of using the NLSSORT function in SQL statements when you want to perform a linguistic comparison instead of a binary comparison. When NLS_COMP is set to LINGUISTIC, SQL operations perform a linguistic comparison based on the value of NLS_SORT. A setting of ANSI is for backward compatibility; in general, you should set NLS_COMP to LINGUISTIC when you want to perform a linguistic comparison.
Set NLS_COMP to LINGUISTIC as follows:
ALTER SESSION SET NLS_COMP = LINGUISTIC;
When NLS_COMP is set to LINGUISTIC, a linguistic index improves the performance of the linguistic comparison. To enable a linguistic index, use the following syntax:
CREATE INDEX i ON t(NLSSORT(col, 'NLS_SORT=FRENCH'));
NLS_SORT
http://docs.oracle.com/cd/B28359_01/olap.111/b28126/dml_options073.htm
http://docs.oracle.com/cd/B28359_01/server.111/b28320/initparams145.htm
NLS_COMP
http://docs.oracle.com/cd/B28359_01/server.111/b28298/ch3globenv.htm#NLSPG231