COUNT number of times prior to specified time, self-join?

问题

For simplicity let's assume I have two tables:

billing with the following fields bill_id (primary, unique key, int), person_id, bill_date, and billing_detail containing bill_id and service_type.

First of all I would like a list of clients (person_id) who were billed for a given range of services in a given period, so simply

SELECT billing.person_id, billing.bill_date
FROM   billing
INNER JOIN billing_detail ON billing.bill_id = billing_detail.bill_id
WHERE      billing_detail.service_type IN (list of services)
  AND      billing.bill_date between some_date and another_date

What I would like to do now is to also show how many times a given client was billed for the same range of services PRIOR to the given date.

Say the billing table contains:

1  | 1 | 1/1/2020
2  | 1 | 1/2/2020
3  | 1 | 1/3/2020
4  | 1 | 1/4/2020
4  | 1 | 2/4/2020

And the billing_detail table contains:

1  |  A
2  |  B
3  |  A
4  |  B
5  |  A

So if I was to run a report for client 1 for the period from January to April for service type A, the expected outcome would be

1 | 1/1/2020 | 0 (no A type service prior to this date)
1 | 1/3/2020 | 1 (One A type service prior to this date)
1 | 2/4/2020 | 2 (Two A type services prior ot this date).

This probably involves some kind of self-join on both tables but my tired bird-brain can't seem to come up with the answer at the moment. Any help would be appreciated.

回答1:

You can use ROW_NUMBER() over the person_id and service_type to get the result you want, subtracting one to start the values at 0:

SELECT person_id, bill_date, service_type,
       ROW_NUMBER() OVER (PARTITION BY person_id, service_type ORDER BY bill_date) - 1 AS prior_services
FROM billing b
JOIN billing_detail bd ON bd.bill_id = b.bill_id

This will give you data for all service types:

person_id   bill_date   service_type    prior_services
1           2020-01-01  A               0
1           2020-01-03  A               1
1           2020-02-04  A               2
1           2020-01-02  B               0
1           2020-01-04  B               1

To restrict the service type, add a

WHERE service_type = 'A'

or similar.

Demo on dbfiddle

来源：https://stackoverflow.com/questions/61586269/count-number-of-times-prior-to-specified-time-self-join

标签

sql

sql-server-2016

self-join