ClickHouse SQL: Accessing Array Elements with ArrayEnumerate for Efficient Data Retrieval

This ClickHouse SQL query aims to retrieve data and calculate a rolling sum of app_count over a 30-day period. However, the original approach using arraySlice and arraySum can be simplified using the arrayEnumerate function to directly access elements within the total_increase array.

The goal is to have each ts value correspond to its respective element in the total_increase array. The original query attempts to achieve this using arraySlice and arraySum to calculate a rolling sum over 30 days. However, a more efficient method is to utilize the arrayEnumerate function to access elements directly from the array.

Here's the optimized query:

SELECT ts, 
    total_increase, 
    total_increase[i] as total_increase_num 
FROM 
  (
    SELECT groupArray(Ds) as t, 
      groupArray(app_count) as total_increase 
    from (
        SELECT min_Ds as Ds, 
          count(distinct AppIdentifier) as app_count 
        FROM (
            select AppIdentifier, 
              min(Ds) as min_Ds 
            from log_iMonkey_iOS_overview 
            GROUP BY AppIdentifier 
          ) 
        GROUP BY min_Ds 
        order by min_Ds 
      ) 
  ) ARRAY 
  JOIN t as ts, 
  arrayEnumerate(t) as i where ts >= toDate('monthly_active_new_business.start')

By replacing the calculation of total_increase_num with total_increase[i], we directly access the corresponding element in the total_increase array using the index provided by arrayEnumerate(t). This approach simplifies the query and improves its performance by eliminating the need for slicing and summing array segments.

This modification ensures that each ts value is associated with its correct total_increase element, streamlining the retrieval and analysis of the data.