选择并加入动态表名称

Question

I would like to get all information about every item . Items has global variable (here on_stock ), but every item has also its own property in different table, and that table has the same name as the items type name.

1. select items
2. join its type_id on types table id -> name
3. join selected item on name .id

Here is the sample:

[items]
 id  | on_stock |  type_id
-----+----------+-----------
  1       1        1(=car)
  2       0        1(=car)
  3       1        2(=ship)
  4       0        2(=ship)

[types]
 id |  name
----+--------
  1     car
  2    ship

[car]
 id | top_speed
----+-----------
 1       200
 2       300

[ship]
 id  | color
-----+-------
 3     red
 4     blue

expected result:

1 on_stock=1 top_speed=200
2 on_stock=0 top_speed=300
3 on_stock=1 color=red
4 on_stock=0 color=blue

Please help to achieve this!

Answer 1

If I could not do it in one request, I'll do it in more(1+item types count).

first, I need the required types as array(id=>name):

$req_types = array();
    $rs = mysql_query("
        SELECT items.type_id,types.name
        FROM items 
        JOIN types ON items.type_id=type.id 
        GROUP BY items.type_id
        ");
    while($type= mysql_fetch_assoc($rs))
        $req_types[$type['id']] = $type['name'];

then I need the common and individual item data:

$groups = array();     
foreach($req_types as $table)
        {
            $rs = mysql_query("
                    SELECT items.*,$table.*
                    FROM items 
                    JOIN $table ON $table.id=items.id
                    ");
            while($item = mysql_fetch_assoc($rs))
                $groups[$table][] = $item;
        }

Answer 2

It isn't pretty, but neither is the data structure. Here is a query to do what you want

SELECT I.id, I.On_stock, C.top_speed,S.Color
FROM ITEMS I
LEFT JOIN Car C ON (I.ID = C.CarID)
LEFT JOIN Ship S ON (I.ID = S.ShipID)

You will have to tweak the query every time you add a new item type, but that is just a downside of this data structure.