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

The way to extract rows from the mysql database is via SELECT. Thus you cannot select rows that do not exist.

What I would do is fill my blog table with all possible dates (for a year, then repeat the process)

 create table blog (
    thedate date not null,
    thetext text null,
    primary key (thedate));

doing a loop to create all dates entries for 2011 (using a program, eg $mydate is the date you want to insert)

  insert IGNORE into blog (thedate,thetext) values ($mydate, null);

(the IGNORE keyword to not create an error (thedate is a primary key) if thedate exists already).
Then you insert the values normally

  insert into blog (thedate,thetext) values ($mydate, "newtext") 
  on duplicate key update thetext="newtext";

Finally to select empty entries, you just have to

  select thedate from blog where thetext is null;