Given different data sources, you will get incomplete data about an event that you need to convert into a minimal representation. To make the problem more concrete, let’s assume a simple table that looks a lot like a clipboard:
CREATE TABLE Events (event_id VARCHAR(25) NOT NULL, start_date DATE NOT NULL, end_date DATE NOT NULL, CHECK (start date < end_date), PRIMARY KEY (event_id, start_date, end_date)); INSERT INTO Events VALUES ('Pie Eating', '2009-01-01', '2009-01-02'), ('Pie Eating', '2009-01-03', '2009-01-05'), ('Pie Eating', '2009-01-04', '2009-01-07'), ('Pie Eating', '2009-02-01', '2009-02-07');
The goal is to reduce these three rows into fewer rows that show how many days we were eating pies.
('Pie Eating', ...