Mysql上个月选择总和（价格）

Question

I have this tables

stk
+---------+--------------+
| Field   | Type         |
+---------+--------------+
| id      | int(11)      | 
| name    | varchar(255) | 
| type_id | int(11)      |
+---------+--------------+

 stk_type

+-------+--------------+
| Field | Type         |
+-------+--------------+
| id    | int(11)      | 
| name  | varchar(255) | 
| price | int(11)      | 
+-------+--------------+

    customer
+-------+--------------+
| Field | Type         | 
+-------+--------------+
| id    | int(11)      | 
| fio   | varchar(255) | 
+-------+--------------+
and sales

+-------------+-----------+
| Field       | Type      | 
+-------------+-----------+
| id          | int(11)   | 
| customer_id | int(11)   |
| stk_id      | int(11)   | 
| date        | timestamp |
+-------------+-----------+

I need to select how much money i got for last month; i don't know how to select it in one query.

SELECT stk_id FROM sales
WHERE date >= DATE_SUB( CURDATE(), INTERVAL 1 MONTH )

So now i have all the stk ids from last month, and i need to count sum, but how can i do it if i have duplicated keys: for example:

If last query returns stk_id 's 1,1,1,2 ,3,3 how can i count the sum if price in stk_type equals next:

id 1 price 100
id 2 price 200
id 3 price 150

so for this example i should get this result 800;

I need to select all the stk_id and somehow to select price and count the sum. Looking for help, thanks.

Answer 1

SELECT sales.stk_id, sum(stk_type.price) 
FROM sales LEFT JOIN stk_type ON (sales.stk_id=stk_type.id) 
WHERE date >= DATE_SUB( CURDATE(), INTERVAL 1 MONTH ) 
GROUP BY sales.stk_id;

I'm assuming "sales.stk_id=stk_type.id" is how they relate?

EDIT: forgot the where clause.

Answer 2

try this sql query

SELECT stk_id, SUM(price) FROM sales
LEFT JOIN stk ON stk_id = stk.id
LEFT JOIN stk_type ON type_id  = stk_type.id
WHERE date >= DATE_SUB( CURDATE(), INTERVAL 1 MONTH )
GROUP BY stk_id