Rails Group By Query

Question

我有這種方法來返回報告。這將返回是這樣的：我得到這個表

+------------+----+---------+--------+----------+ 
| dates | id | name | amount | purchase | 
+------------+----+---------+--------+----------+ 
| 2015-02-10 | 1 | Private | 100 |  30 | 
| 2015-02-10 | 2 | Public | 250 |  45 | 
| 2015-02-20 | 1 | Private | 200 |  20 | 
| 2015-02-20 | 2 | Public | 150 |  25 | 
+------------+----+---------+--------+----------+ 

後，我想在amount申請加價的百分比。日期之間的百分比不同。以下是標記後的表格。 2015-02-10日期，2015-02-20的比例爲10％和20％。

+------------+----+---------+--------+----------+ 
| dates | id | name | amount | purchase | 
+------------+----+---------+--------+----------+ 
| 2015-02-10 | 1 | Private | 110 |  30 | 
| 2015-02-10 | 2 | Public | 275 |  45 | 
| 2015-02-20 | 1 | Private | 240 |  20 | 
| 2015-02-20 | 2 | Public | 180 |  25 | 
+------------+----+---------+--------+----------+ 

這是我的代碼到目前爲止。

def self.report(school_id) 
    items = Transaction.joins("JOIN categories ON categories.id = transactions.category_id") 

    items = items.select("date(from_unixtime(transactions.unix_timestamp)) as dates") 
    items = items.select("categories.id") 
    items = items.select("categories.name") 
    items = items.select("sum(transactions.amount) as amount") 
    items = items.select("avg(transactions.purchase) as purchase") 

    items = items.where("categories.school_id = ?", school_id) 

    items = items.group("categories.id") 
    items = items.group("date(from_unixtime(transactions.unix_timestamp))") 

    items.map do |x| 
    p = Percentage.where(date: 'x[:dates]').limit(1).first.percentage 
    x[:amount] = x[amount] * (100 + p)/100 
    end 

    items 
end 

後標記過程中，我想將它們按id和預期的結果是這樣的。金額將被累計，購買將平均。

+----+---------+--------+----------+ 
| id | name | amount | purchase | 
+----+---------+--------+----------+ 
| 1 | Private | 350 |  25 | 
| 2 | Public | 455 |  35 | 
+----+---------+--------+----------+ 

我弄糊塗瞭如何組通過它，因爲id我試圖用items.group(...)和項目不進行分組。

Answer 1

嘗試改變這一行：

items = items.select("sum(transactions.amount) as amount") 

到

items = items.select("sum(CASE WHEN DATE(dates)=DATE('2015-02-10') THEN transactions.amount*1.1 WHEN DATE(dates)=DATE('2015-02-20') THEN transactions.amount*1.2 ELSE transactions.amount END) as amount")