[Solved]-How to return every nth row from dataset using postgresql to control a Highcharts data series-Highcharts

Use row_number() to enumerate your rows in a subquery (or CTE), and then WHERE (rownum%240)=0. An example using a CTE:

with
original_query as (
SELECT timestamp, interest, yield FROM abc.public.table WHERE symbol='XTC' AND timestamp BETWEEN '2021-06-04 14:51:27.5127' AND '2021-06-11 14:51:27.5127' ORDER BY timestamp
),
numbered as (
select row_number() over () as rownum, oq from original_query oq
),
sampled as (
select (oq).* from numbered where (rownum%240)=0
)
select * from sampled;