How to Add Auto_Increment column to existing Table
It is very simple process to add Auto Increment column to existing table in MySQL. Let's say if you have a table with below definition and there is already some data added to the table.
CREATE TABLE `customer` (
`idcustomer` int,
`firstname` varchar(50) NULL,
`lastname` varchar(30) NULL,
`age` int(11) DEFAULT NULL,
`phonenumber` char(11) DEFAULT NULL,
`dob` date DEFAULT NULL,
`gender` char(1) NOT NULL
) ;
-- Insert sample data
insert into customer(idcustomer,firstname,lastname,age,phonenumber,dob,gender)
values
(1,'Raza','Ali',39,'505-4141969','1980-01-01','M'),
(2,'Aamir','Naz',39,'505-4141969','1980-01-01','M'),
(3,'Aamir','Shahzad',39,'505-4141900','1980-01-01','M'),
(4,'Aamir1','Shahzad',39,'505-4141900','1980-01-01','M'),
(5,'Robert','Ladson',69,'505-345900','1960-01-01','M');
Now if we would like to add "id" column as Auto Increment we can do that by using below statement. Remember that the Auto_Increment column need to be KEY. So you either defined as Primary Key or Unique Key. If your table already have Primary Key then you can defined as UNIQUE KEY.
1) When there is No primary key, then you can define as Primary Key
Alter table customer
add column id int NOT NULL auto_increment UNIQUE Key;
1) When there is No primary key, then you can define as Primary Key
Alter table customer
add column id int NOT NULL auto_increment Primary Key;
2) When there is Already Primary Key, then you can add new auto increment column as UNIQUE KEY.add column id int NOT NULL auto_increment Primary Key;
Alter table customer
add column id int NOT NULL auto_increment UNIQUE Key;
How to add auto increment column to existing table - MySQL Tutorial
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