Question

I have the following tables (removed columns that aren’t used for my examples):

CREATE TABLE `person` (
  `id` int(11) NOT NULL,
  `name` varchar(1024) NOT NULL,
  `sortname` varchar(1024) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `sortname` (`sortname`(255)),
  KEY `name` (`name`(255))
);

CREATE TABLE `personalias` (
  `id` int(11) NOT NULL,
  `person` int(11) NOT NULL,
  `name` varchar(1024) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `person` (`person`),
  KEY `name` (`name`(255))
)

Currently, I’m using this query which works just fine:

select p.* from person p where name = 'John Mayer' or sortname = 'John Mayer';

mysql> explain select p.* from person p where name = 'John Mayer' or sortname = 'John Mayer';
+----+-------------+-------+-------------+---------------+---------------+---------+------+------+----------------------------------------------+
| id | select_type | table | type        | possible_keys | key           | key_len | ref  | rows | Extra                                        |
+----+-------------+-------+-------------+---------------+---------------+---------+------+------+----------------------------------------------+
|  1 | SIMPLE      | p     | index_merge | name,sortname | name,sortname | 767,767 | NULL |    3 | Using sort_union(name,sortname); Using where | 
+----+-------------+-------+-------------+---------------+---------------+---------+------+------+----------------------------------------------+
1 row in set (0.00 sec)

Now I’d like to extend this query to also consider aliases.

First, I’ve tried using a join:

select p.* from person p join personalias a on p.id = a.person where p.name = 'John Mayer' or p.sortname = 'John Mayer' or a.name = 'John Mayer';

mysql> explain select p.* from person p join personalias a on p.id = a.person where p.name = 'John Mayer' or p.sortname = 'John Mayer' or a.name = 'John Mayer';
+----+-------------+-------+--------+-----------------------+---------+---------+-------------------+-------+-----------------+
| id | select_type | table | type   | possible_keys         | key     | key_len | ref               | rows  | Extra           |
+----+-------------+-------+--------+-----------------------+---------+---------+-------------------+-------+-----------------+
|  1 | SIMPLE      | a     | ALL    | ref,name              | NULL    | NULL    | NULL              | 87401 | Using temporary | 
|  1 | SIMPLE      | p     | eq_ref | PRIMARY,name,sortname | PRIMARY | 4       | musicbrainz.a.ref |     1 | Using where     | 
+----+-------------+-------+--------+-----------------------+---------+---------+-------------------+-------+-----------------+
2 rows in set (0.00 sec)

This looks bad: no index, 87401 rows, using temporary. Using temporary only appears when I use distinct, but as an alias might be the same as the name, I can’t really get rid of it.

Next, I’ve tried to replace the join with a subquery:

select p.* from person p where p.name = 'John Mayer' or p.sortname = 'John Mayer' or p.id in (select person from personalias a where a.name = 'John Mayer');

mysql> explain select p.* from person p where p.name = 'John Mayer' or p.sortname = 'John Mayer' or p.id in (select id from personalias a where a.name = 'John Mayer');
+----+--------------------+-------+----------------+------------------+--------+---------+------+--------+-------------+
| id | select_type        | table | type           | possible_keys    | key    | key_len | ref  | rows   | Extra       |
+----+--------------------+-------+----------------+------------------+--------+---------+------+--------+-------------+
|  1 | PRIMARY            | p     | ALL            | name,sortname    | NULL   | NULL    | NULL | 540309 | Using where | 
|  2 | DEPENDENT SUBQUERY | a     | index_subquery | person,name      | person | 4       | func |      1 | Using where | 
+----+--------------------+-------+----------------+------------------+--------+---------+------+--------+-------------+
2 rows in set (0.00 sec)

Again, this looks pretty bad: no index, 540309 rows. Interestingly, both queries (select p.* from person ... or p.id in (4711,12345) and select id from personalias a where a.name = 'John Mayer') work extremely well.

Why doesn’t MySQL use any indices for both of my queries? What else could I do? Currently, it looks best to fetch person.ids for aliases and add them statically as an in(…) to the second query. There certainly has to be another way to do this with a single query. I’m currently out of ideas though. Could I somehow force MySQL into using another (better) query plan?

Answer 1

Try:

SELECT p.* from person p 
WHERE  p.name = 'John Mayer' or p.sortname = 'John Mayer' 

UNION

SELECT p.* from person p, personalias a 
WHERE  p.id =a.person and a.name = 'John Mayer'

UNION will take care of distinctness.