If exists then update else insert I am trying to create a STORED PROCEDURE that will be used to UPDATE a table called machine. This table has three columns (machine_id, machine_name and reg_id).

In aforementioned table,reg_id (INT) is a column whose values can be changed for a machine_id.

I would like to define a QUERY/PROCEDURE to check if a reg_id already exists in that table. If it does, then UPDATE that row, otherwise INSERT a new row. 

Can someone please help me to write that QUERY/PROCEDURE?
Hope This helps, DUPLICATE KEY UPDATE

create table machine(
  machine_id int not null primary key,
  machine_name varchar(50),
  reg_id int
);

insert into machine (machine_id, machine_name, reg_id)
values(1, 'my_machine', 1);

INSERT INTO machine (reg_id, machine_id, machine_name) VALUES (1, 1, 'test_machine')
  ON DUPLICATE KEY UPDATE machine_name=VALUES(machine_name);


Work on SQL Fiddle