Question

我是MySQL数据库优化的新手。

我的查询速度很慢：

   SELECT COUNT(DISTINCT p.product_id) AS total 
     FROM shs_product p 
LEFT JOIN shs_product_description pd 
       ON (p.product_id = pd.product_id) 
LEFT JOIN shs_product_to_store p2s 
       ON (p.product_id = p2s.product_id) 
LEFT JOIN shs_product_to_category p2c 
       ON (p.product_id = p2c.product_id) 
    WHERE pd.language_id = '1' 
      AND p.status = '1' 
      AND p.date_available <= NOW() 
      AND p2s.store_id = '$

有人可以建议关于索引创建的操作来加速这个查询吗？您会推荐哪个表格和哪个列？

非常感谢任何帮助......

Answer 1

三个观察结果：

where子句正在撤消p2s和pd的外部联接。所以你不妨称这些内部连接。
未使用p2c表。因为您正在执行count(distinct)，所以可以删除它。
据推测，ids是整数，所以你不需要引用

因此，查询等效

SELECT COUNT(DISTINCT p.product_id) AS total 
FROM shs_product p JOIN
     shs_product_description pd 
     ON p.product_id = pd.product_id JOIN
     shs_product_to_store p2s 
     ON p.product_id = p2s.product_id 
 WHERE pd.language_id = 1 AND p.status = 1 AND p.date_available <= NOW() AND
       p2s.store_id = '$'

对于此查询，您需要shs_product(status, date_available)上的索引。您还需要用于加入的列和where子句中的索引。我建议：shs_product_description(product_id, language_id)和shs_product_to_store(product_id, store_id)。

最后，假设product_id是product中的唯一索引，您可以使用exists和count(*)代替count(distinct)来表达此查询：

select count(*)
from shs_product p
where p.status = 1 AND p.date_available <= NOW() and
      exists (select 1
              from shs_product_description pd
              where p.product_id = pd.product_id and pd.language_id = 1
             ) and
      exists (select 1
              from shs_product_to_store p2s 
              where p.product_id = p2s.product_id and p2s.store_id = '$'
             );

SELECT COUNT索引

1 个答案: