Restore control file and openresetlogs

Question

hi
When I restore controlfile from autobackup
and than restore database and recover database;
I can only open the database with openresetlogs option.
why?

Answer 1

1-)
Does all datafiles and control files have scn or
checkpoint scn?
and Does all redolog groups have same scn?
what is SCN?
Any changes i.e DML in a database is assigned a system change number (SCN) ,SCN is assigned for changes that is why its called system change number.Both SCN and changes are written to redo log files.
SQL> select current_scn from v$database
  2  /
CURRENT_SCN
     756124
SQL> /
CURRENT_SCN
     756125
SQL> /
CURRENT_SCN
     756136
SQL> /
CURRENT_SCN
     756138
SQL> /
CURRENT_SCN
     756140
SQL> /
CURRENT_SCN
     756394
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area  171966464 bytes
Fixed Size                   787988 bytes
Variable Size             145488364 bytes
Database Buffers           25165824 bytes
Redo Buffers                 524288 bytes
Database mounted.
SQL>  select current_scn from v$database
  2   /
CURRENT_SCN
          0
SQL> /
CURRENT_SCN
          0
SQL> /
CURRENT_SCN
          0
SQL> /
CURRENT_SCN
          0
SQL> When yours database in mount state no activity either from user ends ,background process or foreground process no scn is going to assigned.
whats the use of SCN why it is inremented?
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/consist.htm#CNCPT221
2-)
Does checkpoint scn changes every checkpoint(log switch,etc....).not every second.
checkpoint scn changes after every logswitch cause after log switch an event occur for chekpoint ,this event starts writing dirty buffer from database buffer cache to datafile for which redo log file contains data.After flusing alls dirty buffer from database buffer to datafile an SCN is assigned (system change number assigned) this chekpoint is also a change thats why it is also assigned SCN which is checkpoint SCN,CKPT process gives the database a timestamp/SCN by incrementing a number in controlfile header and broadcast that same SCN to alls datafiles.
CKPT can occur for the number of reason one for is log switch when yours redo log filled , you can also manually trigger checkpoint by issuing alter system command or you may set parameters like log_checkpoint_timeout etc.
3-)
What about scn?? Does it the one that I see from
select current_scn from v$database? which changes every one second?
Check first question reply.
Khurram