在下面尝试

SELECT
   COUNT (start_week_date) AS avg_start_1,
   TIME(
     EXTRACT(hour   FROM AVG(start_time - '0:0:0')), 
     EXTRACT(minute FROM AVG(start_time - '0:0:0')), 
     EXTRACT(second FROM AVG(start_time - '0:0:0'))
   ) as avg_start_time_1
   member_casual
FROM 
   october_fall
WHERE 
   start_week_date = 1
GROUP BY
   member_casual     

另一个选项是

SELECT
   COUNT (start_week_date) AS avg_start_1,
   PARSE_TIME('0-0 0 %H:%M:%E*S', '' || AVG(start_time - '0:0:0')) as avg_start_time_1
   member_casual
FROM 
   october_fall
WHERE 
   start_week_date = 1
GROUP BY
   member_casual