How to inject (append) a windowed average into the output using MS Stream Analytics - azure-stream-analytics

Question

Given a JSON stream that resembles:
{
"timestamp": "2017-01-26T20:27:26.099Z",
"Novato": {
"humidity": "40.996",
"barometric": "1011.2"
},
"Redmond": {
"humidity": "60.832",
"barometric": "1011.8"
}
}
For each City in this object, I want to add a new value called humidity_5_second_avg, which is a 5 second tumbling window average.
But of course for each city, it needs to be unique to that city. And I want to append it to the existing cities' values.
For example:
{
"timestamp": "2017-01-26T20:27:26.099Z",
"Novato": {
"humidity": "40.996",
"barometric": "1011.2",
"humidity_5_second_avg": "38.1234"
},
"Redmond": {
"humidity": "60.832",
"barometric": "1011.8",
"humidity_5_second_avg": "32.1234"
}
}
Is this possible with a Stream Analytics query? Or would I need to create two streams (one with the original data, and one with only average data, and merge them together?

Answer 1

This is tricky to get exactly in the way described. It’s easier to break down city information into one row per city first and then use JOIN.
-- Use CROSS APPLY to split original events into one row per city
WITH CityData AS
(
SELECT
r.PropertyName AS City,
r.PropertyValue.*
FROM localinput i TIMESTAMP BY timestamp
CROSS APPLY GetRecordProperties(i) r
WHERE r.PropertyValue.humidity IS NOT NULL
),
Averages AS
(
SELECT
City,
AVG(humidity) as avg_humidity
FROM CityData
GROUP BY city, TumblingWindow(second, 5)
)
SELECT *, System.Timestamp as ts INTO debug FROM Averages
SELECT
c.*, a.avg_humidity
FROM CityData c
JOIN Averages a
ON c.City = a.City AND DATEDIFF(second, c, a) BETWEEN 0 AND 5