[Oracle SQL] CREATE, ALTER, DROP, TRUNCATE

/*  DDL (Data Definition Language) : Creat문, Drop문, Alter문, Truncate문 */
 
/* Create Table */
 
 create table employees2(
    employee_id number(10),
    name varchar2(20),
    salary number(7,2)
 );
 
 
select * from employees2;
 
 
 
/* 같은 테이블을 동일하게 만들 때 */
 
create table employees3 
as
select * from employees2;
 
 
select * from employees3;
 
 
 
/* Alter - add: 테이블 추가 */
 
alter table employees2 add(
    manager_id varchar2(10)
    );
 
 
select * from employees2;
 
 
 
/* Alter - modify : 테이블 수정 */
 
alter table employees2 modify(
    manager_id varchar2(20)
    );
 
 
 
 
/* Alter - drop column : 칼럼 삭제 */
 
alter table employees2 drop column manager_id;
 
 
select * from employees2;
 
 
 
/* 
    문자형 데이터 
    char, varchar, nchar, nvarchar, long 형태 존재
    long은 최대 2GB가능 
 */
 
/* Drop문 : 테이블 구조를 삭제 */
 
drop table employees2;
 
 
select * from employees2;
 
 
/* Rename */
 
Rename employees3 to employees2;
 
 
desc employees3;
desc employees2;
 
/* Truncate : 테이블 내의 모든 레코드 삭제 */
 
truncate table employees2;
 
 
select * from employees2;