SQL query that returns all dates not used in a table

Question

So lets say I have some records that look like:

2011-01-01 Cat
2011-01-02 Dog
2011-01-04 Horse
2011-01-06 Lion

How can I construct a query

Answer 1

One solution would be to create a separate table with one column to hold all dates from now until eternity (or whenever you expect to stop blogging). For example:

CREATE TABLE Dates (dt DATE);
INSERT INTO Dates VALUES ('2011-01-01');
INSERT INTO Dates VALUES ('2011-01-02');
...etc...
INSERT INTO Dates VALUES ('2099-12-31');

Once this reference table is set up, you can simply outer join to determine the unused dates like so:

SELECT d.dt 
FROM Dates d LEFT JOIN Blogs b ON d.dt = b.dt 
WHERE b.dt IS NULL

If you want to limit the search to two weeks in the future, you could add this to the WHERE clause:

AND d.dt BETWEEN NOW() AND ADDDATE(NOW(), INTERVAL 14 DAY)