获取多对多中未映射记录的数量 table

Question

我有 3 个这样的表

产品

ProductID	ProductDetails
1	...
2	...
3	...

供应商

VendorID	VendorDetails
1	...
2	...
3	...

产品供应商

ProductID	VendorID
1	1
2	1
1	2
2	2
3	2

我将如何找到未映射到特定供应商的产品数量。

我试过了：

SELECT
    COUNT(pr.id) AS product_count
FROM
    products pr
LEFT JOIN vendor_product_map vp ON
    pr.id = vp.product
LEFT JOIN vendors vv ON
    vp.vendor = vv.id
WHERE
    vv.id = 3 AND vp.vendor IS NULL

但这似乎不对。感谢任何帮助

Answer 1

一个简单的 not exists 查询就足够了：

select *
from products
where not exists (
    select *
    from vendor_product_map
    where vendor_product_map.product = product.id
    and vendor_product_map.vendor = 12345678
)

获取多对多中未映射记录的数量 table

Get count of unmapped records in a many-to-many table

mysql

sql

join

mariadb