pgsql database and grouped by half an hour by hour basis packet

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Packet by a half hour

select 

case when substr( to_char(capturetime, 'yyyy-mm-dd hh24:mi'),15, 16) :: integer <=30 
then to_char( capturetime, 'yyyy-mm-dd hh24')||':30' 
else to_char( capturetime, 'yyyy-mm-dd hh24')||':00'
end as row_date2, count(1)

from t_ori_mac_data_xinwangcheng
where capturetime >= '2019-09-03'
group by row_date2 

Grouped by hour

select to_char(capturetime,'hh24'),count(mac)
from  t_ori_mac_data_xinwangcheng 
where capturetime >= '2019-09-03'
group by to_char(capturetime,'hh24')