[sqlite] Summing values by date, returning 0 for missing dates

[Jonathan]

Hi List,
     Let's say I have a table with a simplified structure like this:
/    create table my_table(//
//        time_date DATE,//
//        num INTEGER//
//    );/

     My data has three rows and looks like this:
/    2016-01-01; 3//
//    2016-01-01; 1//
//    2016-01-03; 2/

     I want to return the sum  of "num" for any given time_date, grouped 
by day, so I have:

/       SELECT time_date,//
//              sum( num ) AS sum_num//
//         FROM my_table//
//
//        GROUP BY time_date//
//        ORDER BY time_date ASC/

     This returns:
/    2016-01-01; 4//
//    2016-01-03; 2/

     But what I want is for a value of "0" to be returned for the 
"missing" date 2016-01-02:
/    2016-01-01; 4//
//    2016-01-02; 0//
//    2016-01-03; 2/

     Is this possible? I'm imagining a sub-query with a start and end 
date ("now") but I can't think of how to get SQLite to return data that 
it doesn't have.
     Does anyone have any suggestions for how to achieve this?
     Thanks,
     Jonathan