If you have brought a tablespace offline, now you want to make it available to users again, you can use the ALTER TABLESPACE ... ONLINE statement as shown in the following script:

SQL> connect HR/globalguideline

SQL> CREATE TABLESPACE my_space

2 DATAFILE '/temp/my_space.dbf' SIZE 10M;

Tablespace created.

SQL> ALTER TABLESPACE my_space OFFLINE NORMAL;

Tablespace altered.

...

SQL> ALTER TABLESPACE my_space ONLINE;

Tablespace altered.