mysql> EXPLAIN SELECT `m`.*

    -> FROM

    ->   `Message` AS `m`

    -> LEFT JOIN

    ->   `Person` AS `p` ON (`m`.`person` = `p`.`id`)

    -> WHERE

    ->   'M002649397' IS NULL OR

    ->   `p`.`personId` = 'M002649397';

+----+-------------+-------+--------+---------------+---------+---------+----------------+--------+-------------+

| id | select_type | table | type   | possible_keys | key     | key_len | ref            | rows   | Extra       |

+----+-------------+-------+--------+---------------+---------+---------+----------------+--------+-------------+

|  1 | SIMPLE      | m     | ALL    | NULL          | NULL    | NULL    | NULL           | 273220 |             |

|  1 | SIMPLE      | p     | eq_ref | PRIMARY       | PRIMARY | 8       | pcom.m.person  |      1 | Using where |

+----+-------------+-------+--------+---------------+---------+---------+----------------+--------+-------------+

2 rows in set (0.00 sec)

mysql> EXPLAIN SELECT `m`.*

    -> FROM

    ->   `Message` AS `m`

    -> LEFT JOIN

    ->   `Person` AS `p` ON (`m`.`person` = `p`.`id`)

    -> WHERE

    -> --  'M002649397' IS NULL OR

    ->   `p`.`personId` = 'M002649397';

+----+-------------+-------+-------+--------------------+--------------------+---------+-------+------+-------------+

| id | select_type | table | type  | possible_keys      | key                | key_len | ref   | rows | Extra       |

+----+-------------+-------+-------+--------------------+--------------------+---------+-------+------+-------------+

|  1 | SIMPLE      | p     | const | PRIMARY,personId   | personId           | 767     | const |    1 | Using index |

|  1 | SIMPLE      | m     | ref   | FK9C2397E7A0F6ED11 | FK9C2397E7A0F6ED11 | 9       | const |    3 | Using where |

+----+-------------+-------+-------+--------------------+--------------------+---------+-------+------+-------------+

2 rows in set (0.01 sec)

create table Message (

    type char(1) not null,

    id bigint not null auto_increment,

    createTime datetime not null,

    updateTime datetime not null,

    person bigint,

    primary key (id)

) ENGINE=InnoDB default charset=utf8 collate=utf8_bin;

create table Person (

    id bigint not null auto_increment,

    createTime datetime not null,

    updateTime datetime not null,

    firstName varchar(255),

    lastName varchar(255),

    middleName varchar(255),

    personId varchar(255) not null unique,

    primary key (id)

) ENGINE=InnoDB default charset=utf8 collate=utf8_bin;

create index idx_Message_createTime on Message (createTime);

alter table Message

    add index FK9C2397E7A0F6ED11 (person),

    add constraint FK9C2397E7A0F6ED11

    foreign key (person)

    references Person (id);

create index idx_Person_lastName on Person (lastName);