Тема  ФИО    Время                 Значение 
Плита Иванов 2013-09-12 14:25:01   234
Плита Иванов 2013-09-12 14:25:02   234
Плита Иванов 2013-09-12 14:25:03   234
Плита Иванов 2013-09-12 14:25:04   235
Плита Иванов 2013-09-12 14:25:05   235
Плита Петров 2013-09-12 14:25:01   234

-- Table structure for table `theme`
CREATE TABLE `theme` (
  `name` varchar(20) NOT NULL,
  `id_theme` int(10) unsigned NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id_theme`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

-- Table structure for table `person`
CREATE TABLE `person` (
  `name` varchar(60) NOT NULL,
  `id_theme` int(10) unsigned NOT NULL,
  `id_person` bigint(10) unsigned NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id_person`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

-- Table structure for table `param`
CREATE TABLE `param` (
  `val` bigint(11) NOT NULL,
  `dtime` bigint(13) unsigned NOT NULL, -- время в формате unix_timestamp()
  `id_person` bigint(11) unsigned NOT NULL,
  `id_param` bigint(11) unsigned NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`dtime`,`id_person`),
  UNIQUE KEY `id_param` (`id_param`)
) ENGINE=MyISAM AUTO_INCREMENT=11202 DEFAULT CHARSET=utf8;

 Тема  ФИО    Время                 Значение 
Плита Иванов 2013-09-12 14:25:01   234
Плита Иванов 2013-09-12 14:25:04   235
Плита Петров 2013-09-12 14:25:01   234

select t1.dtime, prs.name, t1.val from param as t1 join person as prs using(id_person)
       join theme on theme.id_theme=prs.id_theme
       where t1.val!= ifnull(
       (select val from param as t2 where t1.id_person=t2.id_person and t2.dtime<t1.dtime order by t2.dtime desc limit 1),-1)
       and theme.name = 'plita' order by id_person, dtime;

`dtime` bigint(13) unsigned NOT NULL, -- время в формате unix_timestamp().

select * from param;
+-----------+-------+-----+----------+
| id_person | dtime | val | id_param |
+-----------+-------+-----+----------+
|         1 |   380 |  10 |        1 |
|         1 |   382 |  10 |        2 |
|         1 |   381 |  10 |        3 |
+-----------+-------+-----+----------+
3 rows in set (0.00 sec)

select t1.*,t2.id_param,t3.id_param
    -> from param t1
    -> left join param t2 on t1.val=t2.val and t1.id_person=t2.id_person and t2.id_param=t1.id_param+1 and t2.dtime>t1.dtime
    -> left join param t3 on t1.val=t3.val and t1.id_person=t3.id_person and t3.id_param=t1.id_param-1 and t3.dtime<t1.dtime
    -> where t3.id_param is null or t2.id_param is null
    -> order by t1.dtime
    -> ;

+-----------+-------+-----+----------+----------+----------+
| id_person | dtime | val | id_param | id_param | id_param |
+-----------+-------+-----+----------+----------+----------+
|         1 |   380 |  10 |        1 |        2 |     NULL |
|         1 |   381 |  10 |        3 |     NULL |     NULL |
|         1 |   382 |  10 |        2 |     NULL |        1 |
+-----------+-------+-----+----------+----------+----------+
3 rows in set (0.00 sec)

mysql> select t1.dtime, prs.name, t1.val from param as t1 join person as prs using(id_person) join theme on theme.id_theme=prs.id_theme
    ->  where t1.val!= ifnull((select val from param as t2 where t1.id_person=t2
.id_person and t2.dtime<t1.dtime order by t2.dtime desc
 ->  limit 1),-1) and theme.name = 'plita' order by id_person, dtime;
+-------+--------+------+
| dtime | name   | val  |
+-------+--------+------+
|   255 | Ivanov |    9 |
|   375 | Ivanov |   10 |
|   388 | Ivanov |   20 |
|   400 | Ivanov |   10 |
|   401 | Ivanov | 5411 |
| 10201 | Ivanov |   11 |
|   100 | Petrov |    9 |
+-------+--------+------+
7 rows in set (2 min 37.30 sec)

mysql> select t1.* from param t1
    -> left join param t2 on t1.val=t2.val and t1.id_person=t2.id_person and t2.id_param=t1.id_param - 1
    -> where  t2.id_param is null;
+-----------+-------+------+----------+
| id_person | dtime | val  | id_param |
+-----------+-------+------+----------+
|         1 |   388 |   20 |        6 |
|         1 |   400 |   10 |        8 |
|         1 |   375 |   10 |        2 |
|         1 |   255 |    9 |        1 |
|         2 |   100 |    9 |        1 |
|         1 | 10201 |   11 |     9009 |
|         1 |   401 | 5411 |        9 |
+-----------+-------+------+----------+
7 rows in set (3 min 36.70 sec)

update param set id_param =(select @a:= @a + 1 from (select @a:= 0) s) order by id_person, dtime 

update param set id_param =(select @a:= @a + 1 from (select @a:= 0) s)  

mysql> explain select t1.dtime, prs.name, t1.val from param as t1 join person as
 prs using(id_person) join theme on theme.id_theme=prs.id_theme
    ->  where t1.val!= ifnull((select val from param as t2 where t1.id_person=t2
.id_person and t2.dtime<t1.dtime order by t2.dtime desc
    ->  limit 1),-1) and theme.name = 'plita' order by id_person, dtime;
+----+--------------------+-------+--------+---------------+---------+---------+
-----------------------+------+---------------------------------+
| id | select_type        | table | type   | possible_keys | key     | key_len |
 ref                   | rows | Extra                           |
+----+--------------------+-------+--------+---------------+---------+---------+
-----------------------+------+---------------------------------+
|  1 | PRIMARY            | theme | system | PRIMARY,name  | NULL    | NULL    |
 NULL                  |    1 | Using temporary; Using filesort |
|  1 | PRIMARY            | prs   | ALL    | PRIMARY       | NULL    | NULL    |
 NULL                  |    2 | Using where                     |
|  1 | PRIMARY            | t1    | ref    | PRIMARY       | PRIMARY | 8       |
 factory.prs.id_person |  100 | Using where                     |
|  2 | DEPENDENT SUBQUERY | t2    | index  | PRIMARY,ind   | ind     | 8       |
 NULL                  |    1 | Using where                     |
+----+--------------------+-------+--------+---------------+---------+---------+
-----------------------+------+---------------------------------+
4 rows in set (0.00 sec)

mysql> explain select t1.* from param t1
    -> left join param t2 on t1.val=t2.val and t1.id_person=t2.id_person and t2.
id_param=t1.id_param - 1
    -> where  t2.id_param is null ;
+----+-------------+-------+------+---------------+---------+---------+---------
-------------+-------+-------------------------+
| id | select_type | table | type | possible_keys | key     | key_len | ref
             | rows  | Extra                   |
+----+-------------+-------+------+---------------+---------+---------+---------
-------------+-------+-------------------------+
|  1 | SIMPLE      | t1    | ALL  | NULL          | NULL    | NULL    | NULL
             | 10011 |                         |
|  1 | SIMPLE      | t2    | ref  | PRIMARY       | PRIMARY | 8       | factory.
t1.id_person |   100 | Using where; Not exists |
+----+-------------+-------+------+---------------+---------+---------+---------
-------------+-------+-------------------------+
2 rows in set (0.00 sec)