只选择日期和年份SQLite

Question

我有一个SQLite数据库结构如下:

ID      Date              Time           Cost
"1" "2016-05-14"    "17:39:35.925973"   "1.98"
"2" "2016-05-14"    "17:39:54.181083"   "2.84"
"3" "2016-05-14"    "17:40:26.408492"   "2.99"
"4" "2016-05-14"    "17:41:28.197353"   "3.39"
"25"    "2016-05-19"    "14:44:27.235790"   "2.5"
"26"    "2016-05-19"    "14:46:35.177696"   "1.58"
"27"    "2016-05-19"    "14:49:12.902651"   "0.1"   
"28"    "2016-05-20"    "21:35:32.446997"   "2.25"  

我想把费用按月和年加起来，不考虑日期。

我在python中做这个，但是我甚至不知道选择月份和年份的sqlite代码。

我试过这个代码:

def SumByMonth():
    usrDate = raw_input('Enter yymm: ')
    dateyear = datetime.datetime.strptime(usrDate, "%y%m").date()
    month_sql = '''SELECT cost FROM Finance WHERE strftime('%m%y', date) = ( ?  )'''
    month_price = [t[0] for t in cur.execute(month_sql, ( dateyear,) )]
    sum_total = sum(month_price)
    print 'sum is for', dateyear,'is', sum_total

我得到的所有结果都是sum is for 2016-05-01 is 0，所以它看起来是在选择当月的第一天，而没有提供一天。我如何选择月份和年份?

谢谢

Answer 1

SQLite没有2位数年份的格式说明符。参考:https://www.sqlite.org/lang_datefunc.html

并且，正如@DanielRoseman提到的:

1. 你混淆了年份和月份，
2. 你不必要地将字符串转换为日期时间。

而不是做的事:

def SumByMonth():
    yyyymm = raw_input('Enter yyyymm: ')
    month_sql = '''SELECT cost FROM Finance WHERE strftime('%Y%m',date) = ?'''
    month_price = [t[0] for t in cur.execute(month_sql,(yyyymm,))]
    sum_total = sum(month_price)
    print 'sum is for', yyyymm,'is', sum_total

更简洁的做法是:

def SumByMonth():
    yyyymm = raw_input('Enter yyyymm: ')
    month_sql = '''SELECT SUM(cost) FROM Finance WHERE strftime('%Y%m',date) = ?'''
    sum_total = cur.execute(month_sql,(yyyymm,)).fetchone()[0]
    print 'sum is for', yyyymm,'is', sum_total