MySql select first rows in every hour, skip rows next 5 minutes

Question

i'm trying to Select only first Rows from Hour as Example as Datetime optional every 2 Hours/3Hours

2020-09-30 09:37:04 SELECT
2020-09-30 09:37:04 SELECT
2020-09-30 09:45:04 SKIP
2020-09-30 09:45:04 SKIP
2020-09-30 09:54:04 SKIP
2020-09-30 10:37:04 SELECT

on other Side i think have a Solution, but its not Work.. maybe Wrong Equal to VAR ?

SET @prev=0;
SELECT `Date`,@prev, @prev:=UNIX_TIMESTAMP(`Date`) 
FROM `tab`
WHERE FLOOR(UNIX_TIMESTAMP(`Date`)/3600)%2 AND UNIX_TIMESTAMP(`Date`)= @prev;```

Answer 1

With NOT EXISTS:

select t.* from tab t
where not exists (
  select 1 from tab 
  where date_format(date, '%Y%m%d%H') = date_format(t.date, '%Y%m%d%H')
    and date < t.date
)

or with RANK() window function:

select date
from (
  select date,
    rank() over (partition by date_format(date, '%Y%m%d%H') order by date) rnk
  from tab
) t
where t.rnk = 1

See the demo.
Results:

> | date                |
> | :------------------ |
> | 2020-09-30 09:37:04 |
> | 2020-09-30 09:37:04 |
> | 2020-09-30 10:37:04 |