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sumForEach

Description​

The ForEach combinator can be applied to the sum aggregate function to turn it from an aggregate function which operates on row values to an aggregate function which operates on array columns, applying the aggregate to each element in the array across rows.

Example usage​

For this example we'll make use of the hits dataset available in our SQL playground.

The hits table contains a column called isMobile of type UInt8 which can be 0 for Desktop or 1 for mobile:

SELECT EventTime, IsMobile FROM metrica.hits ORDER BY rand() LIMIT 10

We'll use the sumForEach aggregate combinator function to analyze how desktop versus mobile traffic varies by hour of the day. Click the play button below to run the query interactively:

SELECT
    toHour(EventTime) AS hour_of_day,
    -- Use sumForEach to count desktop and mobile visits in one pass
    sumForEach([
        IsMobile = 0, -- Desktop visits (IsMobile = 0)
        IsMobile = 1  -- Mobile visits (IsMobile = 1)
    ]) AS device_counts
FROM metrica.hits
GROUP BY hour_of_day
ORDER BY hour_of_day;

See also​