Трюк дня. Агрегирование записей в PostgreSQL. Исходная таблица

WITH projects (task_id, start_date, end_date) 

AS (VALUES 

(1, CAST('10-01-20' AS date), CAST('10-02-20' AS date)), 

(2, CAST('10-02-20' AS date), CAST('10-03-20' AS date)), 

(3, CAST('10-03-20' AS date), CAST('10-04-20' AS date)), 

(4, CAST('10-13-20' AS date), CAST('10-14-20' AS date)), 

(5, CAST('10-14-20' AS date), CAST('10-15-20' AS date)), 

(6, CAST('10-28-20' AS date), CAST('10-29-20' AS date)), 

(7, CAST('10-30-20' AS date), CAST('10-31-20' AS date)))

SELECT * FROM projects;