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.
The following SQL statement defines the “Personid” column to be an auto-increment primary key field in the “Persons” table:
CREATE TABLE Users ( id int NOT NULL AUTO_INCREMENT, LastName varchar(255) NOT NULL, FirstName varchar(255), Age int, PRIMARY KEY (id) );
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.
To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:
ALTER TABLE Persons AUTO_INCREMENT=100;
To insert a new record into the “Persons” table, we will 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');
If you accidentally lose the primary key and need to modify the id column of the table as the primary key, you can use the following SQL statement:
ALTER TABLE Users modify id int(11) AUTO_INCREMENT PRIMARY KEY; ALTER TABLE Users AUTO_INCREMENT=100;