如何提高嵌套的mysql查詢速度，比如這個？

Question

我在執行此類查詢時從mysql服務器檢索快速響應時遇到一些困難：

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詢方法可以提供更快的響應。 Thanx :-)

Answer 1

像這樣的東西：

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