SQLite: Get all dates between dates

问题

I need some help with a SQL (in particular: SQLite) related problem. I have a table 'vacation'

CREATE TABLE vacation(
    name TEXT,
    to_date TEXT, 
    from_date TEXT
);

where I store the date (YYYY-MM-DD), when somebody leaves for vacation and comes back again. Now, I would like to get a distinctive list of all dates, where somebody is on vacation. Let's assume my table looks like:

+------------+-------------+------------+
|    name    |   to_date   |  from_date |
+------------+-------------+------------+
|    Peter   | 2013-07-01  | 2013-07-10 |
|    Paul    | 2013-06-30  | 2013-07-05 |
|    Simon   | 2013-05-10  | 2013-05-15 |
+------------+-------------+------------+

The result from the query should look like:

+------------------------------+
| dates_people_are_on_vacation |
+------------------------------+
|          2013-05-10          |
|          2013-05-11          |
|          2013-05-13          |
|          2013-05-14          |
|          2013-05-15          |
|          2013-06-30          |
|          2013-07-01          |
|          2013-07-02          |
|          2013-07-03          |
|          2013-07-04          |
|          2013-07-05          |
|          2013-07-06          |
|          2013-07-07          |
|          2013-07-08          |
|          2013-07-09          |
|          2013-07-10          |
+------------------------------+

I thought about using a date - table 'all_dates'

CREATE TABLES all_dates(
    date_entry TEXT
);

which covers a 20 year time span (2010-01-01 to 2030-01-01) and the following query:

SELECT date_entry FROM all_dates WHERE date_entry BETWEEN (SELECT from_date FROM vacation) AND (SELECT to_date FROM vacation);

However, If i apply this query on the above dataset, I only get a fraction of my desired result:

+------------------------------+
| dates_people_are_on_vacation |
+------------------------------+
|          2013-07-01          |
|          2013-07-02          |
|          2013-07-03          |
|          2013-07-04          |
|          2013-07-05          |
|          2013-07-06          |
|          2013-07-07          |
|          2013-07-08          |
|          2013-07-09          |
|          2013-07-10          |
+------------------------------+

Can it be done with SQLite? Or it is better, if I just return the 'to_date' and 'from_date' column and fill the gaps between these dates in my Python application?

Any help is appreciated!

回答1:

You can try that:

SELECT date_entry 
FROM vacation 
JOIN all_dates ON date_entry BETWEEN from_date AND to_date
GROUP BY date_entry
ORDER BY date_entry

来源：https://stackoverflow.com/questions/17548964/sqlite-get-all-dates-between-dates

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