Modify Table Structure in Oracle

1. Modify the field data type

Syntax:
Alter table name MODIFY (column name data type );
Eg1:
Alter table emp modify (column1 VARCHAR (10 ));

When modifying the length of a column, you can only edit a longer length than the existing field actually saves, otherwise the following error is prompted: ORA-01441: cannot reduce the column length because some values are too large

2. Add a column

Syntax: alter table name ADD (column name data type); eg1: alter table emp ADD (column1 NUMBER (38,0) not null );

3. Change the list

Syntax: alter table name rename column current COLUMN name TO new COLUMN name; eg1: alter table emp rename column column1 TO column2;

4. delete a column

Syntax: alter table table Name drop column column name; eg1: alter TABLE emp drop COLUMN column1

5. Change the table name

Syntax: alter table current table name rename to new TABLE name; eg1: alter table emp rename to emp_new

6. Add comments to the table

Comment column on table name. column name is 'comment content'; // modify comment on table emp. column1 IS 'comment content'; // Modify table comment