How to calculate visit start time?

This SQL query shows the start time of the session.

Parameters to set in the request

• project-name — the name of the Google BigQuery project containing user session data uploaded via OWOX BI;
• dataset-name — the name of the Google BigQuery dataset containing the session data;
• _TABLE_SUFFIX — the date range you want to view data for.

SQL query

#standardSQL
SELECT
  sessionId,
  TIMESTAMP_MILLIS(timestamp) visitStartTime
FROM (
  SELECT
    sessionId,
    hits.timestamp,
    ROW_NUMBER() OVER(PARTITION BY sessionId ORDER BY hits.timestamp ASC) rowf
  FROM
    `project-name.dataset-name.owoxbi_sessions_*`,
    UNNEST (hits) hits
    WHERE _TABLE_SUFFIX BETWEEN '20191213' AND '20191214'
)
WHERE
  rowf = 1