使用多个子查询连接优化查询

Question

我有一个查询，它从product 表（第一次选择）中获取产品描述，然后将其减去以下子查询语句以获得编号。剩余库存：

-inventory 表中购买的每种产品的总和（第二个）

-sales_detail 表中销售的每种产品的总和（第 3 个）

-转移到stock_transfer表中另一个分支的每个产品的总和（第4个）

-damaged_product 表中损坏的每个产品的总和（第 5 个）

问题是每次加载此查询时，都会对所有 4 个表进行全面搜索以获取 quantity 列的总和。而且随着时间的推移，存储的记录越来越多，查询也会变慢。有什么建议吗？

SELECT p.Id,p.Product_Name Product,p.Description, c.Category_Name Category,sc.Subcategory_Name Subcategory,s.Supplier_Name Supplier, p.Selling_Price `Unit Price`,i.Stocks,s.Sales, i.Stocks - IFNULL(s.Sales, 0) - IFNULL(t.Transfer, 0) - IFNULL(d.Damage, 0) AS Remaining

FROM (SELECT Id, Product_Name, Description, Selling_Price, Category_Id, Subcategory_Id, Supplier_Id       FROM product WHERE enable_flag = 1) p

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(quantity), 0) AS Stocks
                FROM inventory
                WHERE enable_flag = 1 GROUP BY product_id) i ON p.Id = i.product_id

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(quantity), 0) AS Sales
                FROM sales_detail
                WHERE enable_flag = 1 GROUP BY product_id) s USING(product_id)

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(transfer_quantity), 0) AS Transfer
                FROM stock_transfer
                WHERE enable_flag = 1 GROUP BY product_id) t USING(product_id)

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(damaged_quantity), 0) AS Damage
                FROM damaged_product
                WHERE enable_flag = 1 GROUP BY product_id) d USING(product_id)

JOIN Category c ON p.Category_Id=c.Id

JOIN Subcategory sc ON p.Subcategory_Id=sc.Id

JOIN Supplier s ON p.Supplier_Id=s.Id;

Answer 1

使用子查询会阻止使用索引，这会降低查询速度。我建议这样的查询：

SELECT p.*, sc.Subcategory_Name as Subcategory, s.Supplier_Name as Supplier,
       p.Selling_Price as `Unit Price`,
       (SELECT COALESCE(SUM(quantity), 0) 
        FROM inventory i
        WHERE s.enable_flag = 1 AND s.product_id = p.product_id
       ) as stocks,
       (SELECT COALESCE(SUM(quantity), 0) 
        FROM sales_detail sd
        WHERE i.enable_flag = 1 AND i.product_id = p.product_id
       ) as sales,
       (SELECT COALESCE(SUM(tansferquantity), 0) 
        FROM stock_transfer st
        WHERE st.enable_flag = 1 AND st.product_id = p.product_id
       ) as transfers,
       (SELECT COALESCE(SUM(damaged_quantity), 0) 
        FROM damage d
        WHERE d.enable_flag = 1 AND d.product_id = p.product_id
       ) as damaged
FROM product p JOIN
     Category c
     ON p.Category_Id = c.Id JOIN
     Subcategory sc
     ON p.Subcategory_Id = sc.Id JOIN
     Supplier s
     ON p.Supplier_Id = s.Id
WHERE p.enable_flag = 1;

为了提高性能，基础表需要(product_id, enable_flag, quantity) 上的索引。 MySQL 可以在相关子查询中使用索引进行聚合。

我知道您也有计算值。您可能需要在外部查询中进行这些计算，并受到子查询的额外实现的影响。