ORA-01219: database not open: queries allowed on fixed tables/views only

I Am using oracle 11g and SQL developer tool. When i tried to retrieve rows from db i am getting error message as :-

ORA-01219: database not open: queries allowed on fixed tables/views only)

I looked for sgadef.dbf file and it was missing in home directory.. Can someone help me to make it working.

Answer

First of all check the status of the instance you work with (this may need to connect under administrator account):

select status from v$instance;

Probably you will get

STATUS
------------
MOUNTED

Under sys account try to complete

ALTER DATABASE OPEN;

and check that it’s completed successfuly. If not – please share the result of output and alert log in your question.