Changing the Data Type of a Column

The following ALTER TABLE statement changes the data type of the emp.ename column to CHAR:

SQL> CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
  2                    ENAME VARCHAR2(10),
  3                    JOB VARCHAR2(9),
  4                    SAL NUMBER(7, 2),
  5                    DEPTNO NUMBER(2));

Table created.

SQL>
SQL>
SQL> ALTER TABLE emp MODIFY ename CHAR(15);

Table altered.

SQL>

If the table is empty or the column contains null values, you can change the column to any data type. Otherwise, you can change the data type of a column only to a compatible data type. For example, you can change a VARCHAR2 to CHAR but you cannot change a DATE to a NUMBER.

1. Adding a Column
2. Adding a Virtual Column
3. Changing the Size of a Column
4. Changing the Precision of a Numeric Column
5. Changing the Data Type of a Column
6. Changing the Default Value of a Column
7. Dropping a Column