Using Auto Increment

Many databases allow to make the primary key value automatically increment when a new key is added. This ensures that every key is different.

CREATE TABLE Employees (
    Id int NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (Id)
);

CREATE TABLE Employees (
    Id SERIAL PRIMARY KEY
);

CREATE TABLE Employees (
    Id int NOT NULL IDENTITY,
    PRIMARY KEY (Id)
);

CREATE TABLE Employees (
    Id INTEGER PRIMARY KEY    
);

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