mysql - SQL如何计算每月有x笔交易的信用卡数量

Question

我有一个信用卡交易的 MySQL 数据集:

create table trans (
  transdate date,
  card_id int
);

我想知道:

1. how many cards were used to make at least 1 transaction, per month
2. how many cards were used to make at least 5 transactions, per month
3. how many cards were used to make at least 10 transactions, per month
4. how many cards were used to make at least 20 transactions, per month
etc...

因为组重叠，条件聚合似乎是更好的方法:

select sum(cnt >= 1) as trans_1,
       sum(cnt >= 5) as trans_5,
       sum(cnt >= 10) as trans_10,
       sum(cnt >= 20) as trans_20
from (select card_id, count(*) as cnt
      from trans
      group by card_id 
      ) d;

问题是上面总共产生了一个结果集。我想要一个每月的结果集:

year | month | trans_1 | trans_5 | trans_10 | trans_20 | etc
2015 |     1 |       1 |       1 |        0 |        0 | 
2015 |     2 |
2015 |     3 |

我不知道如何在此数据集中按月分组。

Answer 1

如果你想要每月的值，那么你需要在内部和外部查询中按月聚合:

select yr, mon,
       sum(cnt >= 1) as trans_1,
       sum(cnt >= 5) as trans_5,
       sum(cnt >= 10) as trans_10,
       sum(cnt >= 20) as trans_20
from (select year(transdate) as yr, month(transdate) as mon, card_id, count(*) as cnt
      from trans
      group by card_id, year(transdate), month(transdate)
     ) d
group by yr, mon;