DDL

CREATE TABLE nombretabla (
columna1 tipoDato(SIZE) [CONSTRAINT],
...
columnaN tipoDato(SIZE) [CONSTRAINT]
);

Constraints:
NOT NULL - Indicates that a COLUMN cannot store NULL VALUE
UNIQUE - Ensures that each ROW FOR a COLUMN must have a UNIQUE VALUE
PRIMARY KEY - A combination OF a NOT NULL AND UNIQUE. Ensures that a COLUMN (OR combination OF two OR more COLUMNS) have an UNIQUE IDENTITY which helps TO find a particular record IN a TABLE more easily AND quickly
FOREIGN KEY - Ensure the referential integrity OF the DATA IN one TABLE TO MATCH VALUES IN another TABLE
CHECK - Ensures that the VALUE IN a COLUMN meets a specific condition
DEFAULT - Specifies a DEFAULT VALUE WHEN specified NONE FOR this COLUMN

-- EJEMPLO
-- MySQL:

CREATE TABLE Persons
(
P_Id INT NOT NULL,
LastName VARCHAR(255) NOT NULL,
FirstName VARCHAR(255),
Address VARCHAR(255),
City VARCHAR(255),
PRIMARY KEY (P_Id)
)
-- SQL Server / Oracle / MS Access:

CREATE TABLE Persons
(
P_Id INT NOT NULL PRIMARY KEY,
LastName VARCHAR(255) NOT NULL,
FirstName VARCHAR(255),
Address VARCHAR(255),
City VARCHAR(255)
)

-- Clave múltiple
CREATE TABLE Persons
(
P_Id INT NOT NULL,
LastName VARCHAR(255) NOT NULL,
FirstName VARCHAR(255),
Address VARCHAR(255),
City VARCHAR(255),
CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)
)



--                                        -------------CHECK------------

MySQL:

CREATE TABLE Persons
(
P_Id INT NOT NULL,
LastName VARCHAR(255) NOT NULL,
FirstName VARCHAR(255),
Address VARCHAR(255),
City VARCHAR(255),
CHECK (P_Id>0)
)
SQL Server / Oracle / MS Access:

CREATE TABLE Persons
(
P_Id INT NOT NULL CHECK (P_Id>0),
LastName VARCHAR(255) NOT NULL,
FirstName VARCHAR(255),
Address VARCHAR(255),
City VARCHAR(255)
)
TO allow naming OF a CHECK CONSTRAINT, AND FOR defining a CHECK CONSTRAINT ON multiple COLUMNS, USE the following SQL syntax:

MySQL / SQL Server / Oracle / MS Access:

CREATE TABLE Persons
(
P_Id INT NOT NULL,
LastName VARCHAR(255) NOT NULL,
FirstName VARCHAR(255),
Address VARCHAR(255),
City VARCHAR(255),
CONSTRAINT chk_Person CHECK (P_Id>0 AND City='Sandnes')
)


--                                        -------------DROP------------
--Elimina tabla

DROP TABLE

--                                        -------------TRUNCATE------------

TRUNCATE TABLE