非常慢 MySQL 代码（内联和 JOINS）

Question

如何将下面的查询重组为运行更快？运行需要几分钟时间，这会显着降低网络服务器的速度。该查询使用内联查询和连接从多个表中获取产品的详细信息。我觉得一定有更快的方法。

编写以下查询的最有效方式是什么？

SELECT p.*, 
   pd.*, pd.NAME AS NAME, pi.*,p.image AS default_image, 
   (SELECT first FROM  product_shipping psi 
    WHERE  psi.product_id = p.product_id)         AS flat_rate, 
   (SELECT NAME FROM   manufacturer m 
    WHERE  m.manufacturer_id = p.manufacturer_id) AS manufacturer, 
   (SELECT price FROM   product_special ps 
    WHERE  ps.product_id = p.product_id AND ps.customer_group_id = 8) AS special_price 
   FROM   product p 
      LEFT JOIN product_description pd 
          ON ( p.product_id = pd.product_id ) 
      LEFT JOIN product_image pi 
          ON ( p.product_id = pi.product_id ) 
    ORDER  BY p.product_id

Answer 1

您 select 中的很多项目都是重复的，但由于您最初是这样获取数据的，所以我将其保持原样。此外，使用 LEFT JOINs 可能比 INNER JOINs 慢：

SELECT 
    product.*,
    product_description.*,
    product_description.NAME AS NAME,
    product_image.*,
    product.image AS default_image,
    product_shipping.first AS flat_rate,
    manufacturer.NAME AS manufacturer,
    product_special.price AS special_price
FROM
    product
        LEFT JOIN product_description ON product.product_id = product_description.product_id
        LEFT JOIN product_image ON product_image.product_id = product_image.product_id
        LEFT JOIN manufacturer ON product.manufacturer_id = manufacturer.id
        LEFT JOIN product_special ON product.product_id = product_special.product_id AND product_special.customer_group_id = 8
ORDER BY product.product_id

Answer 2

与@Harper 给出的答案不同，我选择进行内部联接，因为您是在内联选择上进行的，所以我的建议是：

 SELECT p.*, 
        pd.*, pd.NAME AS NAME, pi.*,p.image AS default_image, 
        psi.first AS flat_rate, 
        m.NAME AS manufacturer, 
        ps.price AS special_price 
   FROM product p 
       INNER JOIN product_shipping psi 
           ON (psi.product_id = p.product_id)
       INNER JOIN manufacturer m
           ON (m.manufacturer_id = p.manufacturer_id)
       INNER JOIN product_special ps
           ON (ps.product_id = p.product_id AND ps.customer_group_id = 8)
       LEFT JOIN product_description pd 
           ON ( p.product_id = pd.product_id ) 
       LEFT JOIN product_image pi 
           ON ( p.product_id = pi.product_id ) 
 ORDER  BY p.product_id

Answer 3

如果没有索引，则需要索引。想到以下内容：

product_shipping(product_id, first)
manufacturer(manufacturer_id, name)
product_special(product_id, customer_group_id, price)
product_description(product_id)
product_image(product_id)
product(product_id, manufacturer_id)

Re-arranging 如果您没有适当的索引，子查询和连接可能对性能影响不大。

非常慢 MySQL 代码（内联和 JOINS）

Very slow MySQL code (inline and JOINS)

mysql

join

inline