我有3张桌子，如下所示：
products:[product_id,product_name]
stock:[product_id,date,qty_received]
sales:[product_id,date,qty_sold]
我正在尝试通过减去qty_received-qty_sold来显示所有产品的余额。
我的查询是：
SELECT DISTINCT p.product_id, p.product_name,
IFNULL(sum(qty_received),0)-IFNULL(sum(qty_sold),0) as balance FROM products p
LEFT JOIN stock st ON (p.product_id=st.product_id)
LEFT JOIN sales sa ON (p.product_id=sa.product_id)
GROUP BY p.product_id
通过上述查询，我无法获得正确的余额。
能否请你帮忙。
附加信息：
以下是我的表的简化结构
产品表：
CREATE TABLE IF NOT EXISTS `products` (
`product_id` varchar(15) NOT NULL,
`product_name` varchar(20) NOT NULL,
UNIQUE KEY `product_id` (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
-转储表
products的数据INSERT INTO `products` (`product_id`, `product_name`) VALUES
('111', 'Product One'),
('222', 'Product Two'),
('333', 'Product Three'),
('444', 'Product Four');
库存表：
CREATE TABLE IF NOT EXISTS `stock` (
`stock_id` int(11) NOT NULL AUTO_INCREMENT,
`product_id` int(11) NOT NULL,
`qty_received` int(11) NOT NULL,
PRIMARY KEY (`stock_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=112 ;
-转储表
stock的数据INSERT INTO `stock` (`stock_id`, `product_id`, `qty_received`) VALUES
(1, 111, 5),
(2, 222, 10),
(3, 333, 4),
(4, 444, 6),
(5, 111, 2),
(6, 222, 7),
(7, 111, 3),
(8, 111, 3);
销售表
CREATE TABLE IF NOT EXISTS `sales` (
`sales_id` int(11) NOT NULL AUTO_INCREMENT,
`product_id` int(11) NOT NULL,
`qty_sold` int(11) NOT NULL,
PRIMARY KEY (`sales_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=7 ;
-转储表
sales的数据INSERT INTO `sales` (`sales_id`, `product_id`, `qty_sold`) VALUES
(1, 111, -1),
(2, 222, -3),
(3, 333, -2),
(4, 111, -3),
(5, 222, -1),
(6, 222, -4);
我得到的结果是：
+------------+--------------+---------+
| product_id | product_name | balance |
+------------+--------------+---------+
| 111 | Product One | 10 |
| 222 | Product Two | 35 |
| 333 | Product Three| 2 |
| 444 | Product Four | 6 |
+------------+--------------+---------+
我期望正确的平衡是
+------------+--------------+---------+
| product_id | product_name | balance |
+------------+--------------+---------+
| 111 | Product One | 9 |
| 222 | Product Two | 9 |
| 333 | Product Three| 2 |
| 444 | Product Four | 6 |
+------------+--------------+---------+
最终得到了适用于该解决方案的可运行的sql，但不确定这是否是执行此操作的最佳方法。我非常担心性能，因为这些表有大量记录。
SELECT p.product_id,p.product_name,
IFNULL(sum(st.qty_received),0)+IFNULL(sold,0) as balance FROM products p
LEFT JOIN stock st ON (p.product_id=st.product_id)
LEFT JOIN (SELECT sa.product_id,sum(sa.qty_sold) as sold FROM sales sa
GROUP BY sa.product_id) as t1 ON (t1.product_id=p.product_id)
GROUP BY product_id
任何人都可以建议使用更好的sql（或更改架构）以提高速度/性能，以达到库存平衡？
最佳答案
首先，在p.product_name子句中添加GROUP BY。
其次，删除DISTINCT-GROUP BY不必要。
更新
我尝试了几次查询，发现这看起来最简单：
SELECT
p.product_id,
p.product_name,
COALESCE(SUM(qty), 0) as balance
FROM products p
LEFT JOIN (
SELECT product_id, qty_received AS qty FROM stock st UNION ALL
SELECT product_id, qty_sold FROM sales st
) AS T
ON p.product_id = T.product_id
GROUP BY
p.product_id,
p.product_name
另外，我认为使所有表中的
product_id数据类型相同是个好主意。在varchar中是products，在int中是sales/stock。我为你做了一个Fiddle
关于mysql - 获得库存余额，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/10078788/