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".
