mysql - 优化 MySQL 中的多个 JOIN

Question

我有这个 MySQL，它应该是正确的语法:

select c.cat_id,c.cat_name as cat_name, 
 c.cat_desc, c.cat_image, mi.filename, 
 l.link_id, l.user_id, l.address,l.city, 
 l.country,l.link_created,l.link_desc, 
 l.email,l.fax,l.link_hits, l.link_modified,
 l.link_name,l.postcode, l.price,l.link_rating, 
 l.state,l.telephone,l.link_votes,
 l.website, l.link_id, l.link_visited, cf.value
from j25_mt_cats as c,
j25_mt_links as l 
LEFT OUTER JOIN j25_mt_cfvalues AS cf ON (cf.link_id = l.link_id),
j25_mt_images AS mi,
j25_mt_cl as cl
UNION ALL
select c.cat_id,c.cat_name as cat_name, 
 c.cat_desc, c.cat_image, mi.filename, 
 l.link_id, l.user_id, l.address,l.city, 
 l.country,l.link_created,l.link_desc, 
 l.email,l.fax,l.link_hits, l.link_modified,
 l.link_name,l.postcode, l.price,l.link_rating, 
 l.state,l.telephone,l.link_votes,
 l.website, l.link_id, l.link_visited, cf.value
FROM j25_mt_cats as c,
j25_mt_links as l
RIGHT OUTER JOIN j25_mt_cfvalues AS cf ON cf.link_id = l.link_id,
j25_mt_images AS mi,
j25_mt_cl as cl
where cf.cf_id = 40 and cl.link_id = l.link_id 
 AND mi.link_id = l.link_id AND mi.ordering < 2  
 AND c.cat_id = cl.cat_id and c.cat_published = 1 
 AND c.cat_approved = 1 and l.link_published = 1 and l.link_approved = 1
 AND cf.link_id IS NULL;

查询在 tmp 目录中占用了 3GB 以上的空间，最终超时。我在这里遗漏了一些东西，我怎样才能提高效率？我的目标只是添加到现有查询中以从附加表 (j25_mt_cfvalues) 中获取值。

解释:

+----+--------------+------------+-------+---------------+---------+---------+--------------------------+------+------------------+
| id | select_type  | table      | type  | possible_keys | key     | key_len | ref                      | rows | Extra            |
+----+--------------+------------+-------+---------------+---------+---------+--------------------------+------+------------------+
|  1 | PRIMARY      | mi         | ALL   | NULL          | NULL    | NULL    | NULL                     |  165 |                  |
|  1 | PRIMARY      | c          | ALL   | NULL          | NULL    | NULL    | NULL                     |  301 |                  |
|  1 | PRIMARY      | l          | ALL   | NULL          | NULL    | NULL    | NULL                     | 2139 |                  |
|  1 | PRIMARY      | cf         | ref   | link_id       | link_id | 4       | db_table.l.link_id |    2 |                  |
|  1 | PRIMARY      | cl         | index | NULL          | PRIMARY | 4       | NULL                     | 2742 | Using index      |
|  2 | UNION        | NULL       | NULL  | NULL          | NULL    | NULL    | NULL                     | NULL | Impossible WHERE |
| NULL | UNION RESULT | <union1,2> | ALL   | NULL          | NULL    | NULL    | NULL                     | NULL |                  |
+----+--------------+------------+-------+---------------+---------+---------+--------------------------+------+------------------+

j25_mt_cats 模式:

CREATE TABLE j25_mt_cats ( cat_id int(11) NOT NULL auto_increment, cat_name varchar(255) NOT NULL, alias varchar(255) NOT NULL, title varchar(255) NOT NULL, cat_desc text NOT NULL, cat_parent int(11) NOT NULL default '0', cat_links int(11) NOT NULL default '0', cat_cats int(11) NOT NULL default '0', cat_featured tinyint(4) NOT NULL default '0', cat_image varchar(255) NOT NULL, cat_published tinyint(4) NOT NULL default '0', cat_created datetime NOT NULL default '0000-00-00 00:00:00', cat_approved tinyint(4) NOT NULL default '0', cat_template varchar(255) NOT NULL default '', cat_usemainindex tinyint(4) NOT NULL default '0', cat_allow_submission tinyint(4) NOT NULL default '1', cat_show_listings tinyint(3) unsigned NOT NULL default '1', metakey text NOT NULL, metadesc text NOT NULL, ordering int(11) NOT NULL default '0', lft int(11) NOT NULL default '0', rgt int(11) NOT NULL default '0', PRIMARY KEY (cat_id), KEY cat_id (cat_id,cat_published,cat_approved), KEY cat_parent (cat_parent,cat_published,cat_approved,cat_cats,cat_links), KEY dtree (cat_published,cat_approved), KEY lft_rgt (lft,rgt), KEY func_getPathWay (lft,rgt,cat_id,cat_parent), KEY alias (alias) ) ENGINE=MyISAM AUTO_INCREMENT=3851 DEFAULT CHARSET=utf8 |

j25_mt_links 架构:

CREATE TABLE j25_mt_links ( link_id int(11) NOT NULL auto_increment, link_name varchar(255) NOT NULL, alias varchar(255) NOT NULL, link_desc mediumtext NOT NULL, user_id int(11) NOT NULL default '0', link_hits int(11) NOT NULL default '0', link_votes int(11) NOT NULL default '0', link_rating decimal(7,6) unsigned NOT NULL default '0.000000', link_featured smallint(6) NOT NULL default '0', link_published tinyint(4) NOT NULL default '0', link_approved int(4) NOT NULL default '0', link_template varchar(255) NOT NULL, attribs text NOT NULL, metakey text NOT NULL, metadesc text NOT NULL, internal_notes text NOT NULL, ordering int(11) NOT NULL default '0', link_created datetime NOT NULL default '0000-00-00 00:00:00', publish_up datetime NOT NULL default '0000-00-00 00:00:00', publish_down datetime NOT NULL default '0000-00-00 00:00:00', link_modified datetime NOT NULL default '0000-00-00 00:00:00', link_visited int(11) NOT NULL default '0', address varchar(255) NOT NULL, city varchar(255) NOT NULL, state varchar(255) NOT NULL, country varchar(255) NOT NULL, postcode varchar(255) NOT NULL, telephone varchar(255) NOT NULL, fax varchar(255) NOT NULL, email varchar(255) NOT NULL, website varchar(255) NOT NULL, price double(9,2) NOT NULL default '0.00', lat float(10,6) NOT NULL COMMENT 'Latitude', lng float(10,6) NOT NULL COMMENT 'Longitude', zoom tinyint(3) unsigned NOT NULL COMMENT 'Map''s zoom level', PRIMARY KEY (link_id), KEY link_rating (link_rating), KEY link_votes (link_votes), KEY link_name (link_name), KEY publishing (link_published,link_approved,publish_up,publish_down), KEY count_listfeatured (link_published,link_approved,link_featured,publish_up,publish_down,link_id), KEY count_viewowner (link_published,link_approved,user_id,publish_up,publish_down), KEY mylisting (user_id,link_id), FULLTEXT KEY link_name_desc (link_name,link_desc) ) ENGINE=MyISAM AUTO_INCREMENT=3229 DEFAULT CHARSET=utf8 |

j25_mt_cfvalues 架构:

CREATE TABLE j25_mt_cfvalues ( id int(11) NOT NULL auto_increment, cf_id int(11) NOT NULL, link_id int(11) NOT NULL, value mediumtext NOT NULL, attachment int(10) unsigned NOT NULL default '0', counter int(11) NOT NULL default '0', PRIMARY KEY (id), KEY cf_id (cf_id,link_id), KEY link_id (link_id), KEY value (value(8)) ) ENGINE=MyISAM AUTO_INCREMENT=20876 DEFAULT CHARSET=utf8 |

Answer 1

问题是您的第一个 SQL 查询没有任何 WHERE 条件，并且导致您正在处理的每个表都使用全局笛卡尔坐标。仅在第二个查询中应用 WHERE 子句。

就是说，您对 CF 表进行了左连接和右连接，但不能同时使用 cf=40 和 cf IS NULL，因此我简化为仅在 ID AND 40 上进行左连接...所以如果 CF 表中有一条记录，它只显示它的值为 40...任何其他值都将被忽略..

也就是说，您的查询可以简化为单个查询。我还更改为 JOIN 语法而不是 WHERE，这样您和其他人就可以看到与表的关系而不是猜测。

select 
      (all your fields)
   from 
      j25_mt_cats as c
         JOIN j25_mt_cl as cl
            ON c.cat_id = cl.cat_id 
            JOIN j25_mt_links as l 
               ON cl.link_id = l.link_id 
               AND l.link_published = 1 
               AND l.link_approved = 1
               JOIN j25_mt_images AS mi
                 ON l.link_id = mi.link_id 
                AND mi.ordering < 2  
                LEFT OUTER JOIN j25_mt_cfvalues AS cf 
                   ON l.link_id = cf.link_id
                   AND cf.cf_id = 40
   where
          c.cat_published = 1 
      AND c.cat_approved = 1 
   ORDER BY 
      RAND() DESC;

为了帮助优化查询，您的

j25_mt_cats should have an index on (cat_published, cat_approved)
j25_mt_cl on (cat_id)
j25_mt_links on (link_id, link_published, link_approved)
j25_mt_images on (link_id, ordering)
j25_mt_cfvalues on (link_id, cf_id)