text: #standardSQL
  # 16_13: Use of must-revalidate
  SELECT
    client,
    COUNT(0) AS total_requests,
  
    COUNTIF(uses_cache_control) AS total_using_control,
    COUNTIF(uses_revalidate) AS total_revalidate,
  
    ROUND(COUNTIF(uses_cache_control) * 100 / COUNT(0), 2) AS pct_req_using_control,
    ROUND(COUNTIF(uses_revalidate) * 100 / COUNTIF(uses_cache_control), 2) AS pct_control_using_revalidate
  FROM (
    SELECT
      client,
      TRIM(resp_cache_control) != '' AS uses_cache_control,
      REGEXP_CONTAINS(resp_cache_control, r'(?i)(^\s*|,\s*)must-revalidate(\s*,|\s*$)') AS uses_revalidate
    FROM
      `httparchive.almanac.requests`
    WHERE
      date = '2019-07-01'
  )
  GROUP BY
    client
  