mysql - 在 MySQL 中选择分组

Question

我有 2 个表:

'支付'

|id_tax|value|id_currency|
--------------------------
|1     |100  |12         |
|1     |200  |12         |
|1     |300  |13         |
|2     |200  |12         |
|2     |200  |12         |
--------------------------

'评分'

|id_currency|rate|
------------------
|12         |1   |
|13         |6,12|
------------------

什么 SQL 查询会产生这个结果？

|id_tax|value               |
-----------------------------
|1     |100*1+200*1+300*6,12|
|2     |200*1+200*1         |
-----------------------------

Answer 1

SELECT  id_tax, SUM(value * rate)
FROM    pay p
JOIN    rate r
ON      r.id_currency = p.id_currency
GROUP BY
        id_tax