Explain commands

Question

hi,
1)wht is the effect on using following cmds:
alter system
alter session
alter database
how each one differ from each other.
2)when are the situation database shud be mounted.
3)how to identify db startup wth pfile or spfile.
4) what is the difference between initsid.ora & spfileinitsid.ora
plz giv me answer in a simple way.
i went thru the docs i am not able to get it.
so if pos explain the above wth simple example too.
thanks and regards
suresh

Answer 1

hi
1.alter database
Use the ALTER DATABASE statement to modify, maintain, or recover an existing database.
http://www.ss64.com/ora/database_a.html
2.alter system
Use the ALTER SYSTEM statement to dynamically alter your Oracle Database instance. The settings stay in effect as long as the database is mounted.
http://www.ss64.com/ora/system_a.html
http://www.adp-gmbh.ch/ora/sql/alter_system.html
3.alter session
Use the ALTER SESSION statement to set or modify any of the conditions or parameters that affect your connection to the database. The statement stays in effect until you disconnect from the database.
http://www.adp-gmbh.ch/ora/sql/alter_session.html
http://www.ss64.com/ora/session_a.html
4.how to identify db startup wth pfile or spfile.
sql>show parameter spfile
SQL> show parameter spfile;
NAME                                 TYPE        VALUE
spfile                               string      D:\ORACLE\PRODUCT\10.1.0\DB_2\
                                                 DATABASE\SPFILEORCL.ORAif above parameter show value then ur startup by spfile otherwise database using pfile.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> create pfile from spfile;
File created.
SQL> startup pfile=d:\oracle\product\10.1.0\db_2\database\initorcl.ora
ORACLE instance started.
Total System Global Area  171966464 bytes
Fixed Size                   787988 bytes
Variable Size             145488364 bytes
Database Buffers           25165824 bytes
Redo Buffers                 524288 bytes
Database mounted.
Database opened.
SQL> show parameter spfile
NAME                                 TYPE        VALUE
spfile                               string
SQL>
6. what is the difference between initsid.ora & spfileinitsid.ora
initsid.ora file ----- text file
spfile file ------ binary file
for changes in spfile>>
1.alter system ... scope=spfile/both
2.first change in pfile then ///// create spfile ... from pfile /////
http://www.dba-oracle.com/concepts/pfile_spfile.htm
hope this helps.