generate_series() method fails in Redshift

Question

When I run the SQL Query:

 select generate_series(0,g)
 from ( select date(date1) - date(date2) as g from mytable ;

It returns an error:

Answer 1

Why it's not working was explained above. Still, the question "what can we do about this?" is open.

If you develop a BI system on any platform (with generators supported or not), it is very handy to have dimension tables with sequences of numbers and dates. How can you create one in Redshift?

1. in Postgres, produce the necessary sequence using generator
2. export to CSV
3. create a table with the same schema in Redshift
4. import the CSV from Step 2 to Redshift

Imagine you have created a very simple table called calendar:

 id, date
 1, 2017-01-01
 2, 2017-01-02
 ..., ...
 xxx, 2020-01-01

So your query will look like this:

SELECT t.id, t.date_1, t.date_2, c.id as date_id, c.date
FROM mytable t
JOIN calendar c
ON c.date BETWEEN t.date_1::date AND t.date_2::date
ORDER BY 1,4

In calendar table you can also have first dates of week, month, quarter, weekdays (Mon,Tue,etc.), which makes such table super effective for time-based aggregations.