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MySQL AUTO INCREMENT Field


What is an AUTO INCREMENT Field?

Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table.

Often this is the primary key field that we would like to be created automatically every time a new record is inserted.


MySQL AUTO_INCREMENT Keyword

MySQL uses the AUTO_INCREMENT keyword to perform an auto-increment feature.

By default, the starting value for AUTO_INCREMENT is 1, and it will increment by 1 for each new record.

The following SQL statement defines the "Personid" column to be an auto-increment primary key field in the "Persons" table:

CREATE TABLE Persons (
    Personid int NOT NULL AUTO_INCREMENT,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    PRIMARY KEY (Personid)
);

To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:

ALTER TABLE Persons AUTO_INCREMENT=100;

When we insert a new record into the "Persons" table, we do NOT have to specify a value for the "Personid" column (a unique value will be added automatically):

INSERT INTO Persons (FirstName,LastName)
VALUES ('Lars','Monsen');

The SQL statement above would insert a new record into the "Persons" table. The "Personid" column would be assigned a unique value automatically. The "FirstName" column would be set to "Lars" and the "LastName" column would be set to "Monsen".