MySQL的 - 同样的产品

Question

我想这个一些想法的和值：

product_id || tag_id || weight 
-------------------------------- 
4   || 7  || 5 
3   || 7  || 5 
3   || 7  || 5 
3   || 6  || 3 
2   || 4  || 2 
2   || 6  || 3 
1   || 4  || 2 

我需要这样的东西： product_x总重量= Y，使用MySQL。

的行动应该是：

if product_id[rowN] == product_id[rowN+1] 
then sum(weight[rowN] + weight[rowN+1] 

我试图谷歌，荷兰国际集团，但无法找到任何工作。

感谢

Answer 1

GROUP BY clause automatic group all same product ids and sum these weight. 

阅读以了解更多信息http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html

试试这个，

SELECT SUM(weight),product_id from tablename group by product_id 

Answer 2

select product_id, sum(weight) FROM table GROUP BY product_id