DDL (Data Definition Language)

DDL (Data Definition Language) is a language for defining data, or more precisely, 'a language for defining containers that hold data,' and these containers are referred to as objects in a DBMS.
The targets, or object types, that can be defined through DDL are as follows.

DDL Target	Description
Schema	Data structure considering DBMS characteristics and implementation environment, intuitively understood as a single database.
Domain	Information specifying an attribute's data type, size, constraints, etc., understood as the range of values an attribute can hold.
Table	Data storage space
View	A virtual logical table derived from one or more physical tables
Index	Data structure to speed up searches

DDL Commands #

CREATE #

Creates database objects

New Creation

CREATE TABLE <table_name> (
  열이름 데이터 타입 [DEFAULT 값][NOT NULL]
  [PRIMARY KEY (열 리스트)]
  {[FOREIGN KEY(열 리스트) REFERENCES 테이블 이름 [(열 이름)]
  [ ON DELETE 옵션]
  [ ON UPDATE 옵션] ]} * 
  [CHECK (조건식) | UNIQUE (열이름)] ]};
)

Creating a table using information from another table

CREATE TABLE 테이블이름 AS SELECT 문'

ALTER #

Modifies database objects

Add column

ALTER TABLE 테이블이름 ADD 열이름 데이터 타입

Change column data type

ALTER TABLE 테이블이름 MODIFY 열이름 데이터타입

Delete column

ALTER TABLE 테이블이름 DROP 열이름

DROP , TRUNCATE #

DROP : Deletes database objects
TRUNCATE : Deletes the contents of a database object, but retains the table structure

Delete table

DROP TABLE 테이블이름

Delete table contents

TRUNCATE TABLE 테이블이름

Rename table

RENAME TABLE 이전 테이블이름 TO 새로운 테이블이름
ALTER TABLE 이전 테이블이름 RENAME 새로운 테이블 이름

Data Types #

CHAR : Fixed-length string data type
VARCHAR : Variable-length string data type
INT : Data type used for numbers
FLOAT : Floating-point data type
DATE : Data type used for dates