如何计算购销数量之间的差异? [英] How to calculate the difference between purchase and sale quantity?

问题描述

如何使用Ms Access数据库计算一次查询中的购买和销售数量之间的差异?

How can I calculate the difference between the purchase and sale quantity in one query using Ms Access database?

例如，我的数据如下:

ProductId Type Quantity
1         Purchase 24
1         Sale      1

我如何在一个查询中获得(24-1 = 23)的差异?

How would I get the difference of (24-1=23) in one query?

推荐答案

您可以自我加入表格:

SELECT p.productId, (p.quanity - COALESCE(s.quantity, 0)) difference
FROM table p
LEFT JOIN table s
ON p.type = 'Purchase' AND s.type = 'Sale' AND p.productId = s.productId

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