Группировка данных по временным интервалам

WITH ddd AS (SELECT
'2020.12.20 08:00'::TIMESTAMP WITHOUT TIME ZONE AS pBegin,
'2020.12.23 10:00'::TIMESTAMP WITHOUT TIME ZONE AS pEnd
)
SELECT
pBegin +INTERVAL '1 day' * s AS pBeginS,
pEnd -INTERVAL '1 day' *(EXTRACT('day' FROM pEnd - pBegin )::int4 - s)  AS pEndS
FROM generate_series(0, EXTRACT('day' FROM (SELECT pEnd-pBegin FROM ddd))::int4) AS s,
ddd

SELECT EXTRACT('day' FROM '2020.12.23 08:00'::TIMESTAMP - '2020.12.19 10:00'::TIMESTAMP)::int4;
 date_part 
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(1 строка)

WITH ddd AS (
SELECT 
pbegin,
pend,
EXTRACT('day' FROM pend-pbegin)::int4 AS pdays
FROM
(SELECT '2020.12.20 08:00'::TIMESTAMP WITHOUT TIME ZONE AS pbegin, '2020.12.21 10:00'::TIMESTAMP WITHOUT TIME ZONE AS pend) AS dddsrc
) SELECT  
pbegin + INTERVAL '1 day' * s AS sbegin,
pend - INTERVAL '1 day' * (pdays - s) AS send
FROM ddd, generate_series(0, ddd.pdays) AS s;

WITH ddd AS (
SELECT 
pbegin,
pend,
EXTRACT(pPeriod FROM pend-pbegin)::int4 AS pdays
FROM
(SELECT '2020.12.20 19:00'::TIMESTAMP WITHOUT TIME ZONE + INTERVAL '1 microseconds' AS pbegin,  '2020.12.21 18:00'::TIMESTAMP WITHOUT TIME ZONE AS pend, 'day' AS pPeriod) AS dddsrc
) SELECT  
pbegin + INTERVAL '1 day' * s AS sbegin,
pend - INTERVAL '1 day' * (pdays - s) AS send
FROM ddd, generate_series(0, ddd.pdays) AS s;