MySQL的PHP​​ 5表联接

Question

Still learning about MySQL joins at the moment. On one page of my site it shows an inventory, and it needs to pull data from 5 tables to form it.

Currently i do this: (yes its shoddy)

$sql_result4 = mysql_query("SELECT * FROM players WHERE id='$id'", $db); 
$rs4 = mysql_fetch_array($sql_result4)

  if ($rs4[firearm] != "") { 
    $sql_result5 = mysql_query("SELECT icon FROM db_firearms WHERE name='$rs4[firearm]'", $db); 
    $rs5 = mysql_fetch_array($sql_result5); $firearm_icon=$rs5[icon]; $weap = $rs4[firearm];
    }

  if ($rs4[accessory2] != "") {
    $sql_result5 = mysql_query("SELECT icon FROM db_items WHERE name='$rs4[accessory2]'", $db);
    $rs5 = mysql_fetch_array($sql_result5); $item_icon=$rs5[icon]; $access = $rs4[accessory2]; 
    }

  if ($rs4[vehicle2] != "") { 
    $sql_result5 = mysql_query("SELECT icon FROM db_vehicles WHERE name='$rs4[vehicle2]'", $db); 
    $rs5 = mysql_fetch_array($sql_result5); $veh_icon=$rs5[icon]; $veh = $rs4[vehicle2]; 
    }

  if ($rs4[melee2] != "") {
    $sql_result5 = mysql_query("SELECT icon FROM db_melee WHERE name='$rs4[melee2]'", $db); 
    $rs5 = mysql_fetch_array($sql_result5); $mel_icon=$rs5[icon]; $mel = $rs4[melee2]; 
    }

As you can see, this is stupid. I'm guessing I need to combine all that into one, haven't a clue where to start.

Answer 1

SELECT *, db_firearms.icon as firearm_icon, db_items.icon as item_icon, db_vehicles.icon as vehicle_icon, db_melee.icon as melee_icon
FROM players
LEFT JOIN db_firearms  ON (db_firearms.name=firearm)
LEFT JOIN db_items ON (db_items.name=accessory2)
LEFT JOIN db_vehicles ON (db_vehicles.name=vehicle2)
LEFT JOIN db_melee ON (db.melee.name=melee2)
WHERE players.id = $id

Make sure the name field is indexed in all of the tables

Answer 2

i advice you to find a better way then to do 4 JOINS.

because you are multiplying the run time very much.

let say you have 1000 rows in each table (which is not a lot)

the Cartesian multiply will be 1000 * 1000 * 1000 * 1000 * 1000 which is 1000000000000000 , this is the size of the table the server needs to process.

avoid JOINS at all costs

Answer 3

That's not so stupid as it seems. I would change only connected-tables-primary keys from name to id. So you select player and it has firearm_id, accessory_id, vehicle_id and so on. Theese ids are usually numbers. Also this case it's simply to add many-to-many associations if You need.