用其他表中的特定值对表中的行进行计数

Question

I need a quick way to find the Number of items in a table. The items are linked to an other table. Table 1 is products and table 2 is orders.

Orders contains a paid status (1 or 0).

Orders table example:

id paid
1  0
2  1

Products table example:

id orderid type
1  1       5
2  1       5
3  1       3
4  2       5
5  2       5
6  2       3

Products contains a id (orderid) that refers to the order and a type. So i need the number of products where type = 5 and paid = 1 in the orders table.

What is the best and fastest way to archieve this?

So I need all the paid products with type 5. The result should be '2'.

Answer 1

One way is to use a join statement. Making some assumptions about your schema, the following should work:

SELECT COUNT(p.`id`) FROM `products_table` p
LEFT JOIN `orders_table` o ON p.`orderid` = o.`id`
WHERE o.`paid` = 1
AND p.`type` = 5

Answer 2

you can use join like this,

SELECT COUNT(*) AS num_rows 
FROM products 
LEFT JOIN orders ON orders.id = products.orderid 
WHERE type = 5 AND paid = 1