ALTER SESSION

Initialization Parameters and ALTER SESSION

Some initialization parameter are dynamic in the scope of ALTER SESSION. When you set these parameters using ALTER SESSION, the value you set persists only for the duration of the current session.To determine whether a parameter can be altered using an ALTER SESSION statement, query the ISSES_MODIFIABLE column of the V$PARAMETER dynamic performance view.

A number of parameters that can be set using ALTER SESSION are not initialization parameters. You can set them only with ALTER SESSION, not in an initialization parameter file. Those session parameters are described in "Session Parameters and ALTER SESSION".

Session Parameters and ALTER SESSION

The following parameters are session parameters only, not initialization parameters:

CONSTRAINT[S]

Syntax:

CONSTRAINT[S] = { IMMEDIATE | DEFERRED | DEFAULT }

The CONSTRAINT[S] parameter determines when conditions specified by a deferrable constraint are enforced.

• IMMEDIATE indicates that the conditions specified by the deferrable constraint are checked immediately after each DML statement. This setting is equivalent to issuing the SET CONSTRAINTS ALL IMMEDIATE statement at the beginning of each transaction in your session.

• DEFERRED indicates that the conditions specified by the deferrable constraint are checked when the transaction is committed. This setting is equivalent to issuing the SET CONSTRAINTS ALL DEFERRED statement at the beginning of each transaction in your session.

• DEFAULT restores all constraints at the beginning of each transaction to their initial state of DEFERRED or IMMEDIATE.

CURRENT_SCHEMA

Syntax:

CURRENT_SCHEMA = schema

The CURRENT_SCHEMA parameter changes the current schema of the session to the specified schema. Subsequent unqualified references to schema objects during the session will resolve to objects in the specified schema. The setting persists for the duration of the session or until you issue another ALTER SESSION SET CURRENT_SCHEMA statement.

This setting offers a convenient way to perform operations on objects in a schema other than that of the current user without having to qualify the objects with the schema name. This setting changes the current schema, but it does not change the session user or the current user, nor does it give the session user any additional system or object privileges for the session.

ERROR_ON_OVERLAP_TIME

Syntax:

ERROR_ON_OVERLAP_TIME = {TRUE | FALSE}

The ERROR_ON_OVERLAP_TIME parameter determines how Oracle Database should handle an ambiguous boundary datetime value—a case in which it is not clear whether the datetime is in standard or daylight saving time.

• Specify TRUE to return an error for the ambiguous overlap timestamp.

• Specify FALSE to default the ambiguous overlap timestamp to the standard time. This is the default.

Refer to "Support for Daylight Saving Times" for more information on boundary datetime values.

FLAGGER

Syntax:

FLAGGER = { ENTRY | OFF }

The FLAGGER parameter specifies FIPS flagging (as specified in Federal Information Processing Standard 127-2), which causes an error message to be generated when a SQL statement issued is an extension of the Entry Level of SQL-92 (officially, ANSI X3.135-1992, a standard that is now superseded by SQL:2008). FLAGGER is a session parameter only, not an initialization parameter.

After flagging is set in a session, a subsequent ALTER SESSION SET FLAGGER statement will work, but generates the message, ORA-00097. This allows FIPS flagging to be altered without disconnecting the session. OFF turns off flagging.

INSTANCE

Syntax:

INSTANCE = integer

Setting the INSTANCE parameter lets you access another instance as if you were connected to your own instance. INSTANCE is a session parameter only, not an initialization parameter. In an Oracle Real Application Clusters (Oracle RAC) environment, each Oracle RAC instance retains static or dynamic ownership of disk space for optimal DML performance based on the setting of this parameter.

ISOLATION_LEVEL

Syntax:

ISOLATION_LEVEL = {SERIALIZABLE | READ COMMITTED} 

The ISOLATION_LEVEL parameter specifies how transactions containing database modifications are handled. ISOLATION_LEVEL is a session parameter only, not an initialization parameter.

• SERIALIZABLE indicates that transactions in the session use the serializable transaction isolation mode as specified in the SQL standard. If a serializable transaction attempts to execute a DML statement that updates rows currently being updated by another uncommitted transaction at the start of the serializable transaction, then the DML statement fails. A serializable transaction can see its own updates.

• READ COMMITTED indicates that transactions in the session will use the default Oracle Database transaction behavior. If the transaction contains DML that requires row locks held by another transaction, then the DML statement will wait until the row locks are released.

STANDBY_MAX_DATA_DELAY

Syntax:

STANDBY_MAX_DATA_DELAY =  { integer | NONE } 

In an Active Data Guard environment, this session parameter can be used to specify a session-specific apply lag tolerance, measured in seconds, for queries issued by non-administrative users to a physical standby database that is in real-time query mode. This capability allows queries to be safely offloaded from the primary database to a physical standby database, because it is possible to detect if the standby database has become unacceptably stale.

If STANDBY_MAX_DATA_DELAY is set to the default value of NONE, queries issued to a physical standby database will be executed regardless of the apply lag on that database.

If STANDBY_MAX_DATA_DELAY is set to a non-zero value, a query issued to a physical standby database will be executed only if the apply lag is less than or equal to STANDBY_MAX_DATA_DELAY. Otherwise, an ORA-3172 error is returned to alert the client that the apply lag is too large.

If STANDBY_MAX_DATA_DELAY is set to 0, a query issued to a physical standby database is guaranteed to return the exact same result as if the query were issued on the primary database, unless the standby database is lagging behind the primary database, in which case an ORA-3172 error is returned.

TIME_ZONE

Syntax:

TIME_ZONE =  '[+ | -] hh:mm' 
             | LOCAL 
             | DBTIMEZONE 
             | 'time_zone_region'

The TIME_ZONE parameter specifies the default local time zone offset or region name for the current SQL session. TIME_ZONE is a session parameter only, not an initialization parameter. To determine the time zone of the current session, query the built-in function SESSIONTIMEZONE (see SESSIONTIMEZONE).

• Specify a format mask ('[+|-]hh:mm') indicating the hours and minutes before or after UTC (Coordinated Universal Time—formerly Greenwich Mean Time). The valid range for hh:mm is -12:00 to +14:00.

• Specify LOCAL to set the default local time zone offset of the current SQL session to the original default local time zone offset that was established when the current SQL session was started.

• Specify DBTIMEZONE to set the current session time zone to match the value set for the database time zone. If you specify this setting, then the DBTIMEZONE function will return the database time zone as a UTC offset or a time zone region, depending on how the database time zone has been set.

• Specify a valid time_zone_region. To see a listing of valid time zone region names, query the TZNAME column of the V$TIMEZONE_NAMES dynamic performance view. If you specify this setting, then the SESSIONTIMEZONE function will return the region name.

USE_PRIVATE_OUTLINES

Syntax:

USE_PRIVATE_OUTLINES = { TRUE | FALSE | category_name }

The USE_PRIVATE_OUTLINES parameter lets you control the use of private outlines. When this parameter is enabled and an outlined SQL statement is issued, the optimizer retrieves the outline from the session private area rather than the public area used when USE_STORED_OUTLINES is enabled. If no outline exists in the session private area, then the optimizer will not use an outline to compile the statement. USE_PRIVATE_OUTLINES is not an initialization parameter.

• TRUE causes the optimizer to use private outlines stored in the DEFAULT category when compiling requests.

• FALSE specifies that the optimizer should not use stored private outlines. This is the default. If USE_STORED_OUTLINES is enabled, then the optimizer will use stored public outlines.

• category_name causes the optimizer to use outlines stored in the category_name category when compiling requests.

Restriction on USE_PRIVATE_OUTLINES You cannot enable this parameter if USE_STORED_OUTLINES is enabled.

USE_STORED_OUTLINES

Syntax:

USE_STORED_OUTLINES = { TRUE | FALSE | category_name }

The USE_STORED_OUTLINES parameter determines whether the optimizer will use stored public outlines to generate execution plans. USE_STORED_OUTLINES is not an initialization parameter.

• TRUE causes the optimizer to use outlines stored in the DEFAULT category when compiling requests.

• FALSE specifies that the optimizer should not use stored outlines. This is the default.

• category_name causes the optimizer to use outlines stored in the category_name category when compiling requests.

Restriction on USED_STORED_OUTLINES You cannot enable this parameter if USE_PRIVATE_OUTLINES is enabled.

ALTER SESSION ENABLE PARALLEL DML;

ALTER SESSION
   ADVISE COMMIT; 

INSERT INTO employees@remote
   VALUES (8002, 'Juan', 'Fernandez', 'juanf@example.com', NULL, 
   TO_DATE('04-OCT-1992', 'DD-MON-YYYY'), 'SA_CLERK', 3000, 
   NULL, 121, 20); 

ALTER SESSION
   ADVISE ROLLBACK; 

DELETE FROM employees@local
   WHERE employee_id = 8002; 

COMMIT;  

UPDATE jobs@local SET min_salary = 3000
   WHERE job_id = 'SH_CLERK';

COMMIT; 

ALTER SESSION
   CLOSE DATABASE LINK local;

ALTER SESSION 
   SET NLS_DATE_FORMAT = 'YYYY MM DD HH24:MI:SS';

SELECT TO_CHAR(SYSDATE) Today
   FROM DUAL; 

TODAY 
------------------- 
2001 04 12 12:30:38

ALTER SESSION 
   SET NLS_DATE_LANGUAGE = French;

SELECT TO_CHAR(SYSDATE, 'Day DD Month YYYY') Today
   FROM DUAL; 

TODAY 
--------------------------- 
Jeudi    12 Avril     2001

ALTER SESSION
   SET NLS_ISO_CURRENCY = America; 

SELECT TO_CHAR( SUM(salary), 'C999G999D99') Total
   FROM employees; 

TOTAL
------------------
     USD694,900.00

ALTER SESSION SET NLS_NUMERIC_CHARACTERS = ',.' ;

ALTER SESSION SET NLS_CURRENCY = 'FF';

SELECT TO_CHAR( SUM(salary), 'L999G999D99') Total FROM employees;

TOTAL
---------------------
         FF694.900,00

ALTER SESSION
   SET NLS_CURRENCY = 'DM'; 

SELECT TO_CHAR( SUM(salary), 'L999G999D99') Total
   FROM employees; 

TOTAL
---------------------
         DM694.900,00

ALTER SESSION
   SET NLS_LANGUAGE = FRENCH; 

Session modifiee.

SELECT * FROM DMP;

ORA-00942: Table ou vue inexistante

ALTER SESSION
   SET NLS_SORT = XSpanish; 

ALTER SESSION 
   SET SQL_TRACE = TRUE; 

ALTER SESSION SET QUERY_REWRITE_ENABLED = TRUE;