Oracle: how to "unalter" a session parameter? - oracle

Question

I'm doing a case-insensitive query with
alter session set NLS_COMP=LINGUISTIC;
alter session set NLS_SORT=BINARY_CI;
Is there a way to easily capture the session state prior to altering it so that I can restore the session to its original state?

Answer 1

You can obtain the current values using:
select *
from nls_session_parameters;
before you change your session. To restore it, you just use the saved values.
I am not aware of any statement that resets the session parameters to the default value.

Answer 2

The NLS parameters are exposed through a series of views, starting with NLS_. In your case you need NLS_SESSION_PARAMETERS. There are equivalent views for Instance and Database.
This is neater than using v$parameter, although that view does allow us to tell whether a paarmeter is changed from the default value.

Answer 3

You can get the value of a given session parameter by:
SELECT value
FROM nls_session_parameters
WHERE parameter = 'NLS_SORT'; -- replace NLS_SORT with parameter of your choice
This answer demonstrates other means of doing a case insensitive search.
Using UPPER()/LOWER() functions with a function based index.
Regular expressions: REGEXP_LIKE()

Answer 4

You can see the parameter values initially :
SQL> SHOW PARAMETER NLS_SORT;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
nls_sort string BINARY
SQL> SHOW PARAMETER NLS_COMP;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
nls_comp string BINARY
And then set the session parameter accordingly :
SQL> alter session set nls_comp='LINGUISTIC';
Session altered
SQL> alter session set nls_sort='BINARY_CI';
Session altered
In PL/SQL, you can do the following to fetch the parameter value and store it in session variable :
SQL> DECLARE
2 VAR_NLS_SORT VARCHAR2(10);
3 var_nls_comp VARCHAR2(10);
4 BEGIN
5 SELECT VALUE
6 INTO VAR_NLS_SORT
7 FROM NLS_SESSION_PARAMETERS
8 WHERE PARAMETER = 'NLS_SORT';
9 SELECT VALUE
10 INTO VAR_NLS_COMP
11 FROM NLS_SESSION_PARAMETERS
12 WHERE PARAMETER = 'NLS_COMP';
13 DBMS_OUTPUT.PUT_LINE('NLS_SORT = '||VAR_NLS_SORT);
14 DBMS_OUTPUT.PUT_LINE('NLS_COMP = '||VAR_NLS_COMP);
15 END;
16 /
NLS_SORT = BINARY
NLS_COMP = BINARY
PL/SQL procedure successfully completed.
For more information, you can have a look at Oracle – Case Insensitive Sorts & Compares