sql insert into auto increment field code example

Example 1: how to auto increment in sql

CREATE TABLE Persons (
    Personid int NOT NULL AUTO_INCREMENT,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    PRIMARY KEY (Personid)
);
INSERT INTO Persons (FirstName,LastName)
VALUES ('Lars','Monsen');

Example 2: oracle create auto increment column

CREATE TABLE animals (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     PRIMARY KEY (id)
);

INSERT INTO animals (name) VALUES
    ('dog'),('cat'),('penguin'),
    ('lax'),('whale'),('ostrich');

SELECT * FROM animals;
+----+---------+
| id | name    |
+----+---------+
|  1 | dog     |
|  2 | cat     |
|  3 | penguin |
|  4 | lax     |
|  5 | whale   |
|  6 | ostrich |
+----+---------+

Example 3: mysql add auto increment id existing table

ALTER TABLE `users` ADD `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY