Mysql 改进选择连接表查询

Question

I'm trying to get the following behavior:

+-----+--------------+-----+-----+-----+-------+-------+-------+--------+--------+
| id  | name         | hp  | atk | def | spatk | spdef | speed |  type1 |  type2 |
+-----+--------------+-----+-----+-----+-------+-------+-------+--------+--------+
|   1 | Bulbasaur    |  45 |  49 |  49 |    65 |    65 |    45 |  GRASS | POISON |
|   2 | Ivysaur      |  60 |  62 |  63 |    80 |    80 |    60 |  GRASS | POISON |
|   3 | Venusaur     |  80 |  82 |  83 |   100 |   100 |    80 |  GRASS | POISON |
+-----+--------------+-----+-----+-----+-------+-------+-------+--------+--------+

Where 3 tables are defined as the following:

pokedex: 
+----+------------+----+-----+-----+-------+-------+-------+
| id | name       | hp | atk | def | spatk | spdef | speed |
+----+------------+----+-----+-----+-------+-------+-------+
|  1 | Bulbasaur  | 45 |  49 |  49 |    65 |    65 |    45 |
|  2 | Ivysaur    | 60 |  62 |  63 |    80 |    80 |    60 |
|  3 | Venusaur   | 80 |  82 |  83 |   100 |   100 |    80 |
+----+------------+----+-----+-----+-------+-------+-------+

poke_type:
+------------+---------+
| pokedex_id | type_id |
+------------+---------+
|          1 |      13 |
|          1 |       5 |
|          2 |      13 |
|          2 |       5 |
+------------+---------+

type:
+----+----------+
| id | name     |
+----+----------+
|  1 | NONE     |
|  5 | POISON   |
| 13 | GRASS    |
+----+----------+

It's known that each pokedex entry associates with 2 type in the poke_type table. I attempted to make a query like:

USE pokemon;
SELECT  dex.*, 
        t1.name AS type1, 
        t2.name AS type2 
FROM pokedex AS dex, 
    (SELECT pt.pokedex_id AS dexid, t.name AS name 
     FROM pokedex AS d 
          INNER JOIN poke_type AS pt ON d.id = pt.pokedex_id 
          INNER JOIN type as t ON pt.type_id = t.id
    ) AS t1, 
    (SELECT pt.pokedex_id AS dexid, t.name AS name 
     FROM pokedex AS d 
          INNER JOIN poke_type AS pt ON d.id = pt.pokedex_id 
          INNER JOIN type as t ON pt.type_id = t.id
    ) AS t2
WHERE dex.id = t1.dexid AND dex.id = t2.dexid AND t1.name <> t2.name
GROUP BY dex.id -- remove duplicates

It's an ugly query and probably not really efficient. Any idea on how to improve this query/select in a different way?

Answer 1

If it's not important for you which type is type1 and which type is type2, this is probably the simplest you can get:

SELECT  
    dex.*, 
    MAX(t.name) AS type1, 
    MIN(t.name) AS type2 
FROM 
    pokedex AS dex 
    JOIN poke_type AS pt ON dex.id = pt.pokedex_id 
    JOIN type as t ON pt.type_id = t.id
GROUP BY dex.id

sqlfiddle