mysql - 我怎样才能提高嵌套的mysql查询速度，比如这个？

Question

在执行此类查询时，我在从 mysql 服务器检索快速响应时遇到了一些困难：

select distinct(products.id) as product_id,products.title as product_name, (select count(id) from stock where stock.available='0' and stock.product_id=products.id) as none,
(select count(id) from stock where stock.available='1' and stock.product_id=products.id) as available,
(select count(id) from stock where stock.available='2' and stock.product_id=products.id) as staged,
(select count(id) from stock where stock.available='3' and stock.product_id=products.id) as departed,
(select count(id) from stock where stock.available='4' and stock.product_id=products.id) as delivered
from products,stock where products.id=stock.product_id;

我想知道是否有任何其他查询方法可以提供更快的响应。谢谢:-)

Answer 1

Something like this:

SELECT
  P.id as product_id,
  P.title as product_name,
  SUM(CASE WHEN S.available = 0 THEN 1 ELSE 0 END) as none,
  SUM(CASE WHEN S.available = 1 THEN 1 ELSE 0 END) as available,
  SUM(CASE WHEN S.available = 2 THEN 1 ELSE 0 END) as staged,
  SUM(CASE WHEN S.available = 3 THEN 1 ELSE 0 END) as departed,
  SUM(CASE WHEN S.available = 4 THEN 1 ELSE 0 END) as delivered 
FROM products P
      JOIN stock S
          ON P.id = S.product_id
    GROUP BY P.id,
             P.title