1) Remove the field to the field without affecting the data in the existing table:
Alter Table Employee Rename Column Name To Name1;
2) Modify the field type without affecting the data in the existing table (must comply with the conversion rules):
ALTER TABLE RES_RESOURCE_INF MODIFY (Memo Varchar2 (1024));
3) Query the size of the remaining tablespace (for daily check, prevent the table space):
SELECT TABLESPACE_NAME, SUM (BYTES) / 1024/1024 MB from DBA_Free_Space Group by TableSpace_name;
