SQL Option 3: One Table Per Predicate

Here we can support duplicate values.

CREATE TABLE name (  # http://www.w3.org/2000/10/swap/test/demo1/friends-vocab#name
  subject INT NOT NULL,
  object varchar(255),
  INDEX(subject),
  UNIQUE INDEX(subject, object)
);
CREATE TABLE pet (   # http://www.w3.org/2000/10/swap/test/demo1/friends-vocab#pet
  subject INT NOT NULL,
  object INT,
  INDEX(subject),
  UNIQUE INDEX(subject, object)
);
CREATE TABLE type (   # http://www.w3.org/1999/02/22-rdf-syntax-ns#type
  subject INT NOT NULL,
  object INT,
  INDEX(subject),
  UNIQUE INDEX(subject, object)
);
INSERT INTO name VALUES (6, 'Pat Smith');
INSERT INTO name VALUES (6, 'Patrick Smith');
INSERT INTO name VALUES (7, 'Rover');
INSERT INTO pet VALUES (6, 7);
INSERT INTO type VALUES (6, 2);
INSERT INTO type VALUES (7, 3);

mysql> select * from name;                   
+---------+---------------+
| subject | object        |
+---------+---------------+
|       6 | Pat Smith     |
|       6 | Patrick Smith |
|       7 | Rover         |
+---------+---------------+

mysql> select * from pet;
+---------+--------+
| subject | object |
+---------+--------+
|       6 |      7 |
+---------+--------+

mysql> select * from type;
+---------+--------+
| subject | object |
+---------+--------+
|       6 |      2 |
|       7 |      3 |
+---------+--------+