Question

我有桌子：

CREATE TABLE IF NOT EXISTS `bk_cart_rule` (
  `id_cart_rule` int(10) unsigned NOT NULL DEFAULT '0',
  `cart_rule_restriction` tinyint(1) unsigned NOT NULL DEFAULT '0',
  KEY `id_cart_rule` (`id_cart_rule`),
  KEY `cart_rule_restriction` (`cart_rule_restriction`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `bk_cart_rule_combination` (
  `id_cart_rule_1` int(10) unsigned NOT NULL,
  `id_cart_rule_2` int(10) unsigned NOT NULL,
  KEY `id_cart_rule_1` (`id_cart_rule_1`),
  KEY `id_cart_rule_2` (`id_cart_rule_2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


CREATE TABLE IF NOT EXISTS `bk_cart_rule_lang` (
  `id_cart_rule` int(10) unsigned NOT NULL,
  `id_lang` int(10) unsigned NOT NULL,
  KEY `id_cart_rule` (`id_cart_rule`),
  KEY `id_lang` (`id_lang`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

一个查询：

SELECT SQL_NO_CACHE cr.*, crl.*, 1 as selected FROM bk_cart_rule cr 
LEFT JOIN bk_cart_rule_lang crl ON (cr.id_cart_rule = crl.id_cart_rule AND crl.id_lang = 2)

 WHERE cr.id_cart_rule != 375 AND
             (   cr.cart_rule_restriction = 0 OR 
                 cr.id_cart_rule IN ( 
                    SELECT IF(id_cart_rule_1 = 375, id_cart_rule_2, id_cart_rule_1) FROM bk_cart_rule_combination WHERE 375 = id_cart_rule_1 OR 375 = id_cart_rule_2 ) )

明显的优化是：

    SELECT SQL_NO_CACHE DISTINCT cr.*, crl.* 1 as selected FROM bk_cart_rule cr 
LEFT JOIN bk_cart_rule_lang crl ON (cr.id_cart_rule = crl.id_cart_rule AND crl.id_lang = 2) 
LEFT JOIN bk_cart_rule_combination crc ON (375 = crc.id_cart_rule_1 AND  cr.id_cart_rule = crc.id_cart_rule_2) OR (375 = crc.id_cart_rule_2  AND cr.id_cart_rule = crc.id_cart_rule_1)
WHERE  cr.id_cart_rule != 375 AND (cr.cart_rule_restriction = 0 OR NOT ISNULL(crc.id_cart_rule_1))

但是我怎么能摆脱DISTINCT（在bk_cart_rule_combination中我是双向组合:)

id_cart_rule_1 id_cart_rule_2
 375  776
 776  375

或者可能有更好的优化？

Answer 1

如果购物车规则的排序不重要，则添加约束，即第一个的id小于第二个的id。也就是说，按顺序将它们放在表格中。

遗憾的是，MySQL并不允许简单的check约束。相反，您必须以其他方式实现它。这是三个：

实现插入/更新触发器以维护排序（并防止重复）。
在应用程序端实现逻辑。
在存储过程中包装所有数据修改并在存储过程中实现逻辑。

如果您不想解决所有问题（这可能有助于解决其他问题），您可以将select distinct替换为：

group by least(id_cart_rule_1,  id_cart_rule_2), greatest(id_cart_rule_1,  id_cart_rule_2)

Mysql查询优化在没有DISTINCT的情况下转换连接中的子查询

1 个答案: