高效的MySQL查询来查找A中不匹配的条目B

Question

我有两个表（产品和供应商），并且想要查明哪些项目不再列在供应商表中。

表uc_products有产品。表uc_supplier_csv有供应商库存。 uc_products.model加入uc_suppliers.sku。

当试图识别供应商表中未涉及的产品表中的库存时，我看到很长的查询。我只想提取匹配项的nid; sid IS NULL就是这样，我可以识别哪些项目没有供应商。

对于下面的第一个查询，每小时需要数据库服务器（4GB ram/2x 2.4GHz intel）才能得到结果（507行）。我没有等待第二个查询完成。

如何使此查询更优化？是否由于不匹配的字符集？

我在想，下面将是最有效的SQL使用：

  SELECT nid, sid 
      FROM uc_products p 
LEFT OUTER JOIN uc_supplier_csv c 
      ON p.model = c.sku 
     WHERE sid IS NULL ; 

对于此查询，我得到以下EXPLAIN结果：

mysql> EXPLAIN SELECT nid, sid FROM uc_products p LEFT OUTER JOIN uc_supplier_csv c ON p.model = c.sku WHERE sid IS NULL; 
+----+-------------+-------+------+---------------+------+---------+------+--------+-------------------------+ 
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra     | 
+----+-------------+-------+------+---------------+------+---------+------+--------+-------------------------+ 
| 1 | SIMPLE  | p  | ALL | NULL   | NULL | NULL | NULL | 6526 |       | 
| 1 | SIMPLE  | c  | ALL | NULL   | NULL | NULL | NULL | 126639 | Using where; Not exists | 
+----+-------------+-------+------+---------------+------+---------+------+--------+-------------------------+ 
2 rows in set (0.00 sec) 

我会认为密钥idx_sku和idx_model在这里可以使用，但它们不是。是因为表的默认字符集不匹配？一个是UTF-8，另一个是latin1。

我也被认为是这种形式：

SELECT nid 
    FROM uc_products 
WHERE model 
NOT IN ( 
     SELECT DISTINCT sku FROM uc_supplier_csv 
     ) ; 

EXPLAIN显示了该查询的结果如下：

mysql> explain select nid from uc_products where model not in (select sku from uc_supplier_csv) ; 
+----+--------------------+-----------------+-------+-----------------------+---------+---------+------+--------+--------------------------+ 
| id | select_type  | table   | type | possible_keys   | key  | key_len | ref | rows | Extra     | 
+----+--------------------+-----------------+-------+-----------------------+---------+---------+------+--------+--------------------------+ 
| 1 | PRIMARY   | uc_products  | ALL | NULL     | NULL | NULL | NULL | 6520 | Using where    | 
| 2 | DEPENDENT SUBQUERY | uc_supplier_csv | index | idx_sku,idx_sku_stock | idx_sku | 258  | NULL | 126639 | Using where; Using index | 
+----+--------------------+-----------------+-------+-----------------------+---------+---------+------+--------+--------------------------+ 
2 rows in set (0.00 sec) 

而且，这样我就不会错过任何出，这里更多的是一些令人兴奋详细信息：表尺寸和统计，表结构:)

mysql> show table status where Name in ('uc_supplier_csv', 'uc_products') ; 
+-----------------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+---------------------+-------------------+----------+----------------+---------+ 
| Name   | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time   | Update_time   | Check_time   | Collation   | Checksum | Create_options | Comment | 
+-----------------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+---------------------+-------------------+----------+----------------+---------+ 
| uc_products  | MyISAM |  10 | Dynamic | 6520 |    89 |  585796 | 281474976710655 |  232448 |  912 |   NULL | 2009-04-24 11:03:15 | 2009-10-12 14:23:43 | 2009-04-24 11:03:16 | utf8_general_ci |  NULL |    |   | 
| uc_supplier_csv | MyISAM |  10 | Dynamic | 126639 |    26 |  3399704 | 281474976710655 |  5864448 |   0 |   NULL | 2009-10-12 14:28:25 | 2009-10-12 14:28:25 | 2009-10-12 14:28:27 | latin1_swedish_ci |  NULL |    |   | 
+-----------------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+---------------------+-------------------+----------+----------------+---------+ 

和

CREATE TABLE `uc_products` (
    `vid` mediumint(9) NOT NULL default '0', 
    `nid` mediumint(9) NOT NULL default '0', 
    `model` varchar(255) NOT NULL default '', 
    `list_price` decimal(10,2) NOT NULL default '0.00', 
    `cost` decimal(10,2) NOT NULL default '0.00', 
    `sell_price` decimal(10,2) NOT NULL default '0.00', 
    `weight` float NOT NULL default '0', 
    `weight_units` varchar(255) NOT NULL default 'lb', 
    `length` float unsigned NOT NULL default '0', 
    `width` float unsigned NOT NULL default '0', 
    `height` float unsigned NOT NULL default '0', 
    `length_units` varchar(255) NOT NULL default 'in', 
    `pkg_qty` smallint(5) unsigned NOT NULL default '1', 
    `default_qty` smallint(5) unsigned NOT NULL default '1', 
    `unique_hash` varchar(32) NOT NULL, 
    `ordering` tinyint(2) NOT NULL default '0', 
    `shippable` tinyint(2) NOT NULL default '1', 
    PRIMARY KEY (`vid`), 
    KEY `idx_model` (`model`) 
) ENGINE=MyISAM DEFAULT CHARSET=utf8 

CREATE TABLE `uc_supplier_csv` (
    `sid` int(10) unsigned NOT NULL default '0', 
    `sku` varchar(255) default NULL, 
    `stock` int(10) unsigned NOT NULL default '0', 
    `list_price` decimal(8,2) default '0.00', 
    KEY `idx_sku` (`sku`), 
    KEY `idx_stock` (`stock`), 
    KEY `idx_sku_stock` (`sku`,`stock`), 
    KEY `idx_sid` (`sid`) 
) ENGINE=MyISAM DEFAULT CHARSET=latin1 

编辑：从马丁下面几个建议的查询添加查询计划：

mysql> explain SELECT nid FROM uc_products p WHERE NOT EXISTS (SELECT 1 FROM uc_supplier_csv c WHERE p.model = c.sku) ; 
+----+--------------------+-------+-------+---------------+---------+---------+------+--------+--------------------------+ 
| id | select_type  | table | type | possible_keys | key  | key_len | ref | rows | Extra     | 
+----+--------------------+-------+-------+---------------+---------+---------+------+--------+--------------------------+ 
| 1 | PRIMARY   | p  | ALL | NULL   | NULL | NULL | NULL | 6526 | Using where    | 
| 2 | DEPENDENT SUBQUERY | c  | index | NULL   | idx_sku | 258  | NULL | 126639 | Using where; Using index | 
+----+--------------------+-------+-------+---------------+---------+---------+------+--------+--------------------------+ 
2 rows in set (0.00 sec) 

mysql> explain SELECT nid FROM uc_products WHERE model NOT IN (SELECT sku FROM uc_supplier_csv) ; 
+----+--------------------+-----------------+-------+-----------------------+---------+---------+------+--------+--------------------------+ 
| id | select_type  | table   | type | possible_keys   | key  | key_len | ref | rows | Extra     | 
+----+--------------------+-----------------+-------+-----------------------+---------+---------+------+--------+--------------------------+ 
| 1 | PRIMARY   | uc_products  | ALL | NULL     | NULL | NULL | NULL | 6526 | Using where    | 
| 2 | DEPENDENT SUBQUERY | uc_supplier_csv | index | idx_sku,idx_sku_stock | idx_sku | 258  | NULL | 126639 | Using where; Using index | 
+----+--------------------+-----------------+-------+-----------------------+---------+---------+------+--------+--------------------------+ 
2 rows in set (0.00 sec) 

Answer 1

也许尝试使用NOT EXISTS而不是计数？例如：

SELECT nid 
    FROM uc_products p 
WHERE NOT EXISTS ( 
     SELECT 1 
     FROM uc_supplier_csv c 
     WHERE p.model = c.sku 
     ) 

SO用户Quassnoi有short article概述了一些测试，认为这也可能是值得一试：

SELECT nid 
    FROM uc_products 
WHERE model NOT IN ( 
     SELECT sku 
     FROM uc_supplier_csv 
     ) 

基本上按你原来的查询，没有区别。

另一个用于您克里斯，这个时间与编码交叉的帮助下加入：

SELECT nid 
    FROM uc_products p 
WHERE NOT EXISTS (
     SELECT 1 
     FROM uc_supplier_csv c 
     WHERE CONVERT(p.model USING latin1) = c.sku 
     )