C# 求一个表中的值之和，然后将其减去具有相同ID的另一个表中的值之和

我有两张表，库存和取款，都有产品id、数量和金额。我想将库存的所有数量相加，然后将其减去两个表中具有相同产品id的取款单中所有数量的总和。意义

存货清单

product_id | quantity  | amount
1          | 10        | 10000
2          | 20        | 20000
3          | 30        | 30000

撤回

product_id | quantity  | amount
1          | 5         | 5000
2          | 10        | 10000
3          | 20        | 20000

剩余的

product_id | quantity  | amount
1          | 5         | 5000
2          | 10        | 10000
3          | 10        | 10000

到目前为止，我有这个SQL语句，但它给了我错误的信息

"SELECT inventory_tbl.product_id As 'Product ID', SUM(inventory_tbl.quantity) - SUM(withdrawal_tbl.quantity), SUM(inventory_tbl.total) - SUM(withdrawal_tbl.total) 
FROM withdrawal_tbl, inventory_tbl GROUP BY inventory_tbl.product_id"

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谢谢大家!

对所需的输出使用内部联接，请尝试以下操作：

"SELECT inventory_tbl.product_id As 'Product ID', SUM(inventory_tbl.quantity) - SUM(withdrawal_tbl.quantity), SUM(inventory_tbl.total) - SUM(withdrawal_tbl.total) 
FROM inventory_tbl INNER JOIN withdrawal_tbl on inventory_tbl.product_id =withdrawal_tbl.product_id group by inventory_tbl.product_id;"

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你做的是交叉积而不是内部连接，这就是问题所在

将查询更改为类似以下内容

"SELECT inventory_tbl.product_id As 'Product ID', SUM(inventory_tbl.quantity) - SUM(withdrawal_tbl.quantity), SUM(inventory_tbl.total) - SUM(withdrawal_tbl.total) 
FROM withdrawal_tbl inner join inventory_tbl on inventory_tbl.product_id = withdrawal_tbl.product_id  GROUP BY inventory_tbl.product_id"

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预期结果是什么？您得到了哪些错误信息？您使用的是交叉积，而不是内部joininventory\u tbl。总计您是如何获得此值的？是否希望您的

剩余\u tbl

成为您查询的预期结果？