MYSQL优化和问题

Question

我正在尝试优化我的MySQL查询,我需要一些帮助.这是我目前的查询:

SELECT *,
       (SELECT name FROM stores WHERE id = products.store_id) AS store_name,
       (SELECT username FROM stores WHERE id = products.store_id) AS store_username,
       (SELECT region_id FROM stores WHERE id = products.store_id) AS region_id,
       (SELECT city_id FROM stores WHERE id = products.store_id) AS city_id,
       (SELECT name FROM categories_sub WHERE id = products.subcategory_id) AS subcategory_name,
       (SELECT name FROM categories WHERE id = category_id) AS category_name
FROM products
WHERE date_start <= DATE(NOW()) AND date_end >= DATE(NOW())

我很确定它可以更快.

我也有一个问题,当我尝试按region_id选择所有产品时(通过添加类似"AND region_id = MYID"的东西)它不起作用,我想知道它是否可以让它工作,以及如何？

感谢您的时间!

解

这是我的最终查询,如果它可以帮助任何人:

SELECT p.*,
       s.name AS store_name,
       cs.name AS subcategory_name,
       cat.id AS category_id, cat.name AS category_name,
       c.id AS city_id, c.name AS city_name,
       r.id AS region_id, r.name AS region_name
  FROM products p
       JOIN stores s ON (s.id = p.store_id)
       JOIN categories_sub cs ON (cs.id = p.subcategory_id)
       JOIN categories cat ON (cat.id = cs.category_id)
       JOIN cities c ON (c.id = s.city_id)
       JOIN regions r ON (r.id = c.region_id)
  WHERE DATE(NOW()) BETWEEN p.date_start AND p.date_end

谢谢!

Answer 1

你真的需要学会使用JOIN.它是关系查询的基本操作,就像while()循环是大多数应用程序语言中的基本控制结构一样.

任何有关SQL的书籍或教程都应该涵盖JOIN.

SELECT p.*, 
 s.name AS store_name, s.username AS store_username, 
 s.region_id, s.city_id,
 cs.name AS subcategory_name,
 c.name AS category_name
FROM products p
 JOIN stores s ON (s.id = p.store_id)
 JOIN categories c ON (c.id = p.category_id)
 JOIN categories_sub cs ON (cs.id = p.subcategory_id)
WHERE DATE(NOW()) BETWEEN p.date_start AND p.date_end

现在,您可以为WHERE子句添加更多条件:

  AND s.region_id = ?;

还有一个评论......我试图通过使用BETWEEN谓词来聪明,但这可能会混淆MySQL相对简单的优化器.MySQL可能更容易优化原始语法:

WHERE p.date_start <= DATE(NOW()) AND p.date_end >= DATE(NOW())