SQL：累積相加與插入到表

Question

考慮SQL表

Date  || Visits || Purchases 
20120403   2    1 
20120925   1    0 
20130101   1    1 
20130405   1    0 
20130916   1    0 

我想追加一個列，它是爲年訪問的累計總和，對於購買的累積和列爲年和最後一列，找出累計購買和訪問之間的比例。因此

我的期望表是

Date  || Visits || Purchases || CumVisits || CumPurchases || Ratio 
20120403   2    1    2    1   1/2 
20120925   1    0    3    1   1/3 
20130101   1    1    1    1   1/1 
20130405   1    0    2    1   1/2 
20130916   1    0    3    1   1/3 

我將如何完成累計列的插入和它們在sqlite的平均？

Answer 1

SELECT 
    t.Date, 
    t.Visits, 
    t.Purchases, 
    SUM(r.Visits) AS CumVisits, 
    SUM(r.Purchases) AS CumPurchases, 
    SUM(r.Purchases)*1.0/SUM(r.Visits) AS Ratio 
FROM t 
JOIN t AS r ON r.Date BETWEEN SUBSTR(t.DATE, 1, 4) AND t.Date 
GROUP BY t.Date 

SQLFiddle