联接两个表。 一列使用SUM

Question

I need a little help with a MySQL query.

I have two tables one table is a list of product and one table is a list of warehouses quantity

product:

product_id   product_name
1            name1
2            name2
3            name3

warehouse_product

id   warehouse_id   product_id   product_quantity
1    1              1            15
2    2              1            30
3    1              2            100
4    2              2            30
5    1              3            20
6    2              3            40

The results Im looking to get from the above data would be

product_id   product_name  product_quantity
1            name1         45
2            name2         130
3            name3         60

I've tried many query but it's not working. My query is:

SELECT 
    product_id as product_id, SUM(quantity) as quantity
FROM
    (SELECT 
        p.product_id as product_id, wp.product_quantity as quantity
    FROM
        product as p
    LEFT JOIN warehouse_product as wp ON p.product_id = wp.product_id
    WHERE
        product_active = 1)

Answer 1

Try this:

SELECT p.product_id, p.product_name, SUM(wp.quantity) as quantity 
FROM product as p 
LEFT JOIN warehouse_product as wp 
ON p.product_id = wp.product_id 
AND product_active = 1
GROUP BY p.product_id, p.product_name

After JOINing the two tables you need to use GROUP BY so that SUM of quantity can be calculated for each product.

Answer 2

SELECT P.productid, 
       P.ProductName, 
       Sum(W.product_quantity) As quantity
FROM   Product AS P 
       LEFT JOIN warehouse_product AS W 
              ON P.productid = W.productid 
GROUP  BY P.ProductId , P.ProductName

SQLFiddle

Answer 3

select p.product_id,p.product_name,sum(product_quantity) as 'product_quantity'
from product p inner join warehouse_product whp on
whp.product_id=p.product_id group by whp.product_id

Answer 4

select p.product_id, p.product_name,sum(w.product_quantity)
from 
product p
inner join
warehouse_product w
on
p.product_id = w.product_id

group by w.product_id
order by p.product_name;