create a simple BigQuery table if the table does not exist

if_table_exists.sql

CREATE TABLE IF NOT EXISTS `testing.insert` AS
  (
 
  SELECT
    date,
    COUNT(DISTINCT(visitid)) AS unique_visits
  FROM
    `bigquery-public-data.google_analytics_sample.ga_sessions_*`
  WHERE
    _table_suffix = '20170801'
  GROUP BY
    1) ;