ORDER BY中的MySQL rand（）函数

Question

I have legacy code that has sql query, now i need to optimize that query because it is taking too long (14 sec) in production server. I'm still unsure where to begin. Especially in rand() function because it seems has performance issue

SELECT
      order_detail.product_id,
      dtb_products.name,
      dtb_products.main_list_image,
      dtb_products_price.price01_min,
      dtb_products_price.price01_max,
      dtb_products_price.price02_min,
      dtb_products_price.price02_max,
      dtb_products.limited_flag,
      dtb_products.limited_start_date,
      dtb_products.limited_end_date
    FROM
      dtb_order
    INNER JOIN
      (SELECT 
         dtb_order_2.customer_id 
       FROM  
         dtb_order AS  dtb_order_2
       INNER JOIN
         dtb_order_detail
       ON
         dtb_order_detail.order_id = dtb_order_2.order_id 
       WHERE 
         dtb_order_detail.product_id = 1256
       GROUP BY
         dtb_order_2.customer_id 
      ) AS CUSTOMER

    ON
      dtb_order.customer_id = CUSTOMER.customer_id
    INNER JOIN 
      (SELECT 
         dtb_order_detail.product_id,
         dtb_order_detail.order_id
       FROM  
         dtb_order_detail
       INNER JOIN
         dtb_products
       ON
         dtb_products.product_id = dtb_order_detail.product_id
       WHERE 
         dtb_order_detail.product_id <> 1256 AND dtb_products.del_flg = 0 AND dtb_products.status = 1
      ) AS order_detail
    ON
      order_detail.order_id = dtb_order.order_id
    LEFT JOIN 
      (
       SELECT product_id as product_id_sub,
              MIN(price01) AS price01_min,
              MAX(price01) AS price01_max,
              MIN(price02) AS price02_min,
              MAX(price02) AS price02_max
       FROM dtb_products_class 
       GROUP BY product_id
      ) AS dtb_products_price 
    ON 
       order_detail.product_id = dtb_products_price.product_id_sub
    LEFT JOIN 
      dtb_products
    ON
      dtb_products.product_id = order_detail.product_id
    GROUP BY
      order_detail.product_id
    ORDER BY
      rand() 
    limit 
      8;

Where should I begin to optimize that query?

I have read several blog posts, one of them is http://explainextended.com/2009/03/01/selecting-random-rows/ but i'm still figuring out how to implement that method in query above.

I really appreciate your help.

Thank you

EDIT

The requirement is :

fetch products ids of those were bought with a fixed product id, eg 1256 and then fetch each of these products info, including from the price table.

EDIT

tables in query

dtb_order , dtb_order_detail , dtb_products , dtb_products_class

Answer 1

I does not read your question body, but as usual, I do limit 80, save sql result set into some cached storage (you can use json encode, or serialize, and put content in file), and when you need, get it from your storage, and get 8 random items from this. Also, think about cache storage reset function, when you will add some data to your table.