How to fill in rows based on event type data

问题

So my table has 2 columns: hour and customerID. Every customer will have 2 rows, one corresponding to hour that he/she came into the store, and one corresponding to hour that he/she left the store. With this data, I want to create a table that has every hour that a customer has been in the store. For example, a customer X entered the store at 1PM and left at 5PM, so there would be 5 rows (1 for each hour) like the screenshot below.

Here's my attempt that's now:

select
    hour
    ,first_value(customer_id) over (partition by customer_id order by hour rows between unbounded preceding and current row) as customer_id
FROM table 

回答1:

Assuming that:

• you are running Postgres

• a given customer always has exactly two rows in the table

• hour is of a date-like datatype

Then one option is to use generate_series() with a lateral join, like so:

select t.customer_id, x.hour
from (
    select customer_id, min(hour) min_hour, max(hour) max_hour 
    from mytable 
    group by customer_id
) t
cross join lateral generate_series(min_hour, max_hour, '1 hour') x(hour)
order by t.customer_id, x.hour

Demo on DB Fiddlde:

customer_id | hour               
:---------- | :------------------
X           | 2019-04-01 13:00:00
X           | 2019-04-01 14:00:00
X           | 2019-04-01 15:00:00
X           | 2019-04-01 16:00:00
X           | 2019-04-01 17:00:00
Y           | 2019-04-01 17:00:00
Y           | 2019-04-01 18:00:00
Y           | 2019-04-01 19:00:00

来源：https://stackoverflow.com/questions/61879511/how-to-fill-in-rows-based-on-event-type-data