How to deadlock MySQL

gistfile1.sql

-- Setup the following schema
CREATE TABLE `seq` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(11) NOT NULL,
  `value` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name_idx` (`name`)
) ENGINE=InnoDB;


-- In process 1
set autocommit = 0;
select * from seq where name = 'foo' for update;

-- In process 2
set autocommit = 0;
select * from seq where name = 'foo' for update;

-- In process 1
insert into seq (name, value) values ('foo', 1);
-- process 1 will now block 

-- In process 2
insert into seq (name, value) values ('foo', 1);

-- Process 2 will deadlock & will allow process 1 to continue

This is meant to describe why you encounter deadlocks sometimes when you don't expect to