1. Start - run cmd;
2.
sqlplus /nolog, and then use sys to connect to the database: conn sys/oracle as sysdba;
3、select name from v$datafile
select name from v$datafile;
4.
Find the data file directory you deleted by mistake, and then use alter database datafile 'd:\oracle\product\10.2.0\db_1\database\data file name' offline drop; if drop is omitted, ora-01145 may appear : Immediate offline is not allowed error unless media recovery is enabled
5.
After the above execution is successful, finally use alter database open; just open the database.