Oracle PL/SQL/Table/Change Column Type

Alter table: change existing column type

   <source lang="sql">

SQL> SQL> -- create demo table SQL> create table Employee(

 2    ID                 VARCHAR2(4 BYTE)         NOT NULL,
 3    First_Name         VARCHAR2(10 BYTE),
 4    Last_Name          VARCHAR2(10 BYTE),
 5    Start_Date         DATE,
 6    End_Date           DATE,
 7    Salary             Number(8,2),
 8    City               VARCHAR2(10 BYTE),
 9    Description        VARCHAR2(15 BYTE)
10  )
11  /

Table created. SQL> SQL> SQL> -- display data in the table SQL> select * from Employee

 2  /

no rows selected SQL> SQL> SQL> SQL> Alter table employee modify ( id number,

 2                                 Start_Date varchar2(255)
 3   );

Table altered. SQL> SQL> desc employee;

Name                        Null?    Type
--------------------------- -------- -----------------
ID                          NOT NULL NUMBER
FIRST_NAME                   VARCHAR2(10)
LAST_NAME                    VARCHAR2(10)
START_DATE                   VARCHAR2(255)
END_DATE                     DATE
SALARY                       NUMBER(8,2)
CITY                         VARCHAR2(10)
DESCRIPTION                  VARCHAR2(15)

SQL> SQL> SQL> SQL> SQL> -- clean the table SQL> drop table Employee

 2  /

Table dropped. SQL> SQL>

      </source>