gistfile1.txt

mysql>CREATE TABLE articles (
    ->   id int unsigned not null auto_increment,
    ->   blog_id int,
    ->   article_id int,
    ->   pbody mediumtext,
    ->   primary key(id),
    ->   unique key (blog_id, article_id),
    ->   fulltext key (pbody)
    -> ) engine = mroonga default charset = utf8;
Query OK, 0 rows affected (0.81 sec)

mysql>INSERT INTO articles (blog_id,article_id,pbody) VALUES (1, 100,"foo bar bas");
Query OK, 1 row affected (0.40 sec)

mysql>INSERT INTO articles (blog_id,article_id,pbody) VALUES (1, 100,"foo bar bas");
ERROR 1062 (23000): Duplicate entry '1-100' for key 'blog_id'

mysql>UPDATE articles SET pbody="foo bar bbbbbzzz" where blog_id=1 and article_id=100;
Query OK, 0 rows affected (0.11 sec)
Rows matched: 0  Changed: 0  Warnings: 0

この時点でおかしい?

mysql>INSERT INTO articles (blog_id,article_id,pbody) VALUES (2, 100,"foo bar bas");
Query OK, 1 row affected (0.15 sec)

mysql>select * from articles where blog_id=1 and article_id=100;
Empty set (0.05 sec)