Question

我需要弄清楚两个表之间的匹配数量。

目前，我正在使用此查询，这会导致找到匹配的次数。

SELECT count(*) FROM products WHERE EXISTS (SELECT 1 FROM inventory WHERE products.products_id = inventory.product_id) AND products.orders_id = 'xxx'

如果有5个产品，其中3个可以在另一个表中找到 - 它返回＆＃34; 3.

我需要能够知道总共有多少行以及有多少行匹配 - 就像找到了3/5。我该怎么做？

Answer 1

如果产品在库存中是唯一的，那么“正常”方式是：

SELECT count(*) as total, count(i.product_id) as matches
FROM products p LEFT JOIN
     inventory i
     ON p.products_id = i.product_id
WHERE p.orders_id = 'xxx';

如果inventory可以有重复项，那么一个简单的方法是：

SELECT count(distinct p.product_id) as total, count(i.product_id) as matches
FROM products p LEFT JOIN
     inventory i
     ON p.products_id = i.product_id
WHERE p.orders_id = 'xxx';

编辑：

如果您需要考虑数量：

SUM(CASE WHEN i.qty > 0 THEN 1 ELSE 0 END)

Answer 2

让我们试试这个

SELECT count(u.Product_id) as total, count(i.product_id) as matches
FROM products p 
LEFT  JOIN inventory i ON p.products_id = i.product_id
RIGHT JOIN inventory u ON p.products_id = u.product_id
WHERE p.orders_id = 'xxx';

MySQL - 从两个表中查找多少匹配（如6/9找到）

2 个答案: