Bigquery - SQL for Flattening Custom Metrics Value

Google Analytics stream data into bigquery in a nested json format, it make sometimes difficult for the users to flatten custom metrics data for each event, this can be overcome by using below custom dimension temp function (Standard SQL only). We can pass customMetrics.index and customMetrics.value as parameter for temp function.

CREATE TEMP FUNCTION
  customMetricByIndex(indx INT64,
    arr ARRAY<STRUCT<index INT64,
    value INT64>>) AS ( (
    SELECT
      x.value
    FROM
      UNNEST(arr) x
    WHERE
      indx=x.index) );

    SELECT visitStarttime, visitId, visitNumber,
    hit.hitNumber AS session_hit_count,
    hit.type AS hit_type,
    hit.page.hostname url_domain_name,
    hit.page,
    customMetricByIndex(3,  hit.customMetrics) AS custom_metrics_1
  FROM
    `project.dataset.ga_sessions_20180909`,
    UNNEST(hits) AS hit