MYSQL optimize & questions

问题

I am trying to optimize my MySQL queries and I need some help. Here is my current query :

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())

I am pretty sure it can be faster.

I also have a problem, when I try to select all products by region_id (by adding something like "AND region_id = MYID") it doesn't work, and I wonder if it's possible to get it working, and how?

Thank you for your time!

Solution

Here is my final query, if it can help anyone :

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

Thanks!

回答1:

You really need to learn to use JOIN. It's a fundamental operation for relational queries, just as a while() loop is a basic control structure in most application languages.

Any book or tutorial on SQL should cover 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

Now you can add more conditions to your WHERE clause:

  AND s.region_id = ?;

One more comment... I was trying to be clever by using the BETWEEN predicate, but this might confuse MySQL's relatively simple optimizer. MySQL might have an easier time optimizing your original syntax:

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

回答2:

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

来源：https://stackoverflow.com/questions/763667/mysql-optimize-questions

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sql

mysql

optimization

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