Running total with lag
Each train line corresponds to a value of train_id. For each stop of the line for each line, calculate how long it takes for the train to travel from the previous stop to the current stop. Then, sum this over each line to obtain the amount of time it takes for the train to travel from the head of the line to each stop along the way.
Bu egzersiz, kursun bir parçasıdır
Time Series Analysis in PostgreSQL
Uygulamalı etkileşimli egzersiz
Bu egzersizi bu örnek kodu tamamlayarak deneyin.
-- Fetch the previous arrival time
SELECT
train_id,
station,
arrival_time,
___ ___ (
___
ORDER BY arrival_time) AS previous_arrival_time
FROM train_schedule
ORDER BY train_id, arrival_time;