MySQL: FULL OUTER JOIN - How do I merge one column?

SELECT 
COALESCE(t1.id, t2.id) as id,
t1.value1,
t2.value2
FROM table1 t1
FULL JOIN table2 t2 ON t1.id = t2.id;

Use:

    SELECT t1.id,
           t1.value,
           t2.value2 
      FROM table1 t1
 LEFT JOIN table2 t2 ON t2.id = t1.id
UNION
    SELECT t2.id,
           t1.value,
           t2.value2
      FROM TABLE1 t1
RIGHT JOIN TABLE2 t2 ON t2.id = t1.id

The UNION operator removes row/record duplicates, so you have to define/list the columns appropriately.

Scripts:

DROP TABLE IF EXISTS `example`.`table1`;
CREATE TABLE  `example`.`table1` (
  `id` int(10) unsigned NOT NULL default '0',
  `value` varchar(45) NOT NULL default ''
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSERT INTO table1 VALUES (1, 'a'), (2, 'c'), (3, 'e');

DROP TABLE IF EXISTS `example`.`table2`;
CREATE TABLE  `example`.`table2` (
  `id` int(10) unsigned NOT NULL default '0',
  `value2` varchar(45) NOT NULL default ''
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSERT INTO table2 VALUES (1, 'b'), (3, 'd'), (4, 'f');

Edit: Fixed line above