第一个唯一的 Sql 行

Question

I have a MySql table of users order and it has columns such as:

user_id | timestamp   | is_order_Parent | Status |

1       | 10-02-2020  |     N           |   C    |
2       | 11-02-2010  |     Y           |   D    |
3       | 11-02-2020  |     N           |   C    |
1       | 12-02-2010  |     N           |   C    |
1       | 15-02-2020  |     N           |   C    |
2       | 15-02-2010  |     N           |   C    |

I want to count number of new custmer per day defined as: a customer who orders non-parent order and his order status is C AND WHEN COUNTING A USER ONCE IN A DAY WE DONT COUNT HIM FOR OTHER DAYS

An ideal resulted table will be:

Timestamp: Day | Distinct values of User ID

10-02-2020     |     1
11-02-2010     |     1
12-02-2010     |     0  <--- already counted user_id = 1 above, so no need to count it here
15-02-2010     |     1

table name is cscart_orders

Answer 1

If you are running MySQL 8.0, you can do this with window functions an aggregation:

select timestamp, sum(timestamp = timestamp0) new_users
from (
    select 
        t.*, 
        min(case when is_order_parent = 'N' and status = 'C' then timestamp end) over(partition by user_id) timestamp0
    from mytable t
) t
group by timestamp

The window min() computes the timestamp when each user became a "new user". Then, the outer query aggregates by date, and counts how many new users were found on that date.

A nice thing about this approach is that it does not require enumerating the dates separately.

Answer 2

You can use two levels of aggregation:

select first_timestamp, count(*)
from (select t.user_id, min(timestamp) as first_timestamp
      from t
      where is_order_parent = 'N' and status = 'C'
      group by t.user_id
     ) t
group by first_timestamp;