Sql - query taking long - mysql

Question

I have two tables. One is called map_life, and the second one is called scripts. The map_life table has a lot of rows, that are identified by a column called lifeid. The rows at the table scripts are identified by the column objectid. I want to create a query that gets all the rows from the table map_life and also adds the column scriptfrom scripts table if lifeidmatches objectid, and that the objecttype is npc.
I created the following query.
SELECT id
,lifeid
,x_pos
,y_pos
,foothold
,min_click_pos
,max_click_pos
,respawn_time
,flags
,script.script
FROM map_life life
LEFT JOIN scripts script
ON script.objectid = life.lifeid
AND script.script_type = 'npc'
However, that query takes a lot of time. Any way I can tune it? Thanks.
EDIT: I have ran EXPLAIN command, there are the results.
"id","select_type","table","type","possible_keys","key","key_len","ref","rows","Extra"
1,"SIMPLE","life","ALL","","","","",47600,""
1,"SIMPLE","script","ref","PRIMARY","PRIMARY","1","const",1834,"Using where"
EDIT 2: Here are the create statmenets of each table.
map_life
DROP TABLE IF EXISTS `mcdb`.`map_life`;
CREATE TABLE `mcdb`.`map_life` (
`id` bigint(21) unsigned NOT NULL AUTO_INCREMENT,
`mapid` int(11) NOT NULL,
`life_type` enum('npc','mob','reactor') NOT NULL,
`lifeid` int(11) NOT NULL,
`life_name` varchar(50) DEFAULT NULL COMMENT 'For reactors, specifies a handle so scripts may interact with them; for NPC/mob, this field is useless',
`x_pos` smallint(6) NOT NULL DEFAULT '0',
`y_pos` smallint(6) NOT NULL DEFAULT '0',
`foothold` smallint(6) NOT NULL DEFAULT '0',
`min_click_pos` smallint(6) NOT NULL DEFAULT '0',
`max_click_pos` smallint(6) NOT NULL DEFAULT '0',
`respawn_time` int(11) NOT NULL DEFAULT '0',
`flags` set('faces_left') NOT NULL DEFAULT '',
PRIMARY KEY (`id`,`lifeid`) USING BTREE,
KEY `lifetype` (`mapid`,`life_type`)
) ENGINE=InnoDB AUTO_INCREMENT=47557 DEFAULT CHARSET=latin1;
scripts
DROP TABLE IF EXISTS `mcdb`.`scripts`;
CREATE TABLE `mcdb`.`scripts` (
`script_type` enum('npc','reactor','quest','item','map','map_enter','map_first_enter') NOT NULL,
`helper` tinyint(3) NOT NULL DEFAULT '-1' COMMENT 'Represents the quest state for quests, and the index of the script for NPCs (NPCs may have multiple scripts).',
`objectid` int(11) NOT NULL DEFAULT '0',
`script` varchar(40) NOT NULL DEFAULT '',
PRIMARY KEY (`script_type`,`helper`,`objectid`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COMMENT='Lists all the scripts that belong to NPCs/reactors/etc. ';

Answer 1

You should probably add an index to the 'script_type' field depending on the type. If it's not using a type that can be indexed, you should change the type if possible and index
Here is a link that discusses more about indexes with MySQL, http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html

Answer 2

Your primary key on scripts is:
PRIMARY KEY (`script_type`,`helper`,`objectid`)
The order of multi-column keys is important.
From the docs:
Any index that does not span all AND levels in the WHERE clause is not
used to optimize the query. In other words, to be able to use an
index, a prefix of the index must be used in every AND group.
Your primary key on scripts does include both the script_type and objectid columns, which are both used in the join's ON clause:
ON script.objectid = life.lifeid
AND script.script_type = 'npc'
but the primary key also includes the helper column between those two, so MySQL can only use the primary key index for searching using the first column (script_type).
So, for every join, MySQL must search through all scripts records where script_type is 'npc' to find the particular objectid record to join on.
MySQL could full utilize the primary key index if your ON clause included all three columns like this:
ON script.objectid = life.lifeid
AND script.helper = 1
AND script.script_type = 'npc'
If you often query the scripts table without specifying the helper column, consider changing the order of the columns in the primary key to put the helper column last:
PRIMARY KEY (`script_type`,`objectid`,`helper`)
Then, your original ON clause is appropriate for the index because the index prefix includes all of the columns in your predicate (script_type,objectid):
ON script.objectid = life.lifeid
AND script.script_type = 'npc'
Alternatively, add an additional index with just the two columns mentioned in the ON clause:
KEY `scrypt_type_objectid` (`script_type`,`objectid`)