Oracle Column Operations
Add a column:
ALTER TABLE Emp4 Add test varchar2 (10);
Modify a column:
ALTER TABLE Emp4 Modify Test varchar2 (20);
Delete a column:
ALTER TABLE emp4 drop column test;
Here to pay attention to a few places, first of all, add and modify columns do not need to add a keyword column, or will be an error ora-00905.
Second, to delete a single column, be sure to add column, and then remember that deletion is not required to add columns type.
The practice is as follows;
Add multiple columns:
ALTER TABLE Emp4 Add (Test varchar2), test2 number);
Modify multiple columns:
ALTER TABLE Emp4 Modify (Test varchar2 (a), test2 varchar2 (20));
Delete multiple columns:
ALTER TABLE Emp4 drop (TEST,TEST2);
Very strange phenomenon, and then a single column to add the keyword column, but then delete more columns, you cannot add column keyword.