按月分组，日期时间为 sql

Question

halo i want to count the data and group by month (month start date) then show in date time, any idea?

table_a

timestamp
2020-11-28 04:00:00
2020-11-28 05:00:00
2020-12-29 01:00:00
2020-12-29 02:00:00
2020-12-29 03:00:00

expected result:

timestamp             count
2020-11-01 00:00:00     2
2020-12-01 00:00:00     3

my query is:

SELECT STR_TO_DATE(DATE_FORMAT(timestamp, '%Y-%m-dd HH'), '%Y-%m-dd HH'), count(*) as count
from table_a

but my results was:

timestamp    count
2020-11-00     2
2020-12-00     3

Answer 1

You can use:

select str_to_date(concat_ws('-', year(timestamp), month(timestamp), 1)) as yyyymm,
       count(*)
from table_a
group by yyyymm;

Answer 2

i fixed the question with add group by month(timestamp) , im ignored the minuted, the important things is group by month, here are my full query:

SELECT timestamp, count(*) as count
from table_a 
group by month(timestamp)

then the output show:

timestamp             count
2020-11-01 04:00:00     2
2020-12-01 01:00:00     3