Question

I have the following query:

  SELECT timestamp,
         COUNT(*)
    FROM table
GROUP BY timestamp

But some timestamps do not show up because there is no data. Here’s an example

1:00:00 |  3
1:00:02 | 17
1:00:03 |  2

Notice that 1:00:01 is missing. Is there a way to make the 1:00:01 | 0 appear in the result?

Answer 1

MySQL doesn’t have recursive functionality, so you’re left with using the NUMBERS table trick –

1. Create a table that only holds incrementing numbers – easy to do using an auto_increment:

   DROP TABLE IF EXISTS `example`.`numbers`;
   CREATE TABLE  `example`.`numbers` (
     `id` int(10) unsigned NOT NULL auto_increment,
      PRIMARY KEY  (`id`)
   ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
   

2. Populate the table using:

   INSERT INTO NUMBERS
     (id)
   VALUES
     (NULL)
   

   …for as many values as you need.

3. Use DATE_ADD to construct a list of times, increasing the seconds based on the NUMBERS.id value:

   SELECT x.*
     FROM (SELECT DATE_FORMAT(DATE_ADD('2010-01-01', INTERVAL n.id - 1 SECOND), '%T') 
             FROM numbers n) x
   

4. LEFT JOIN onto your table of data based on the time portion:

      SELECT x.ts AS timestamp,
             COALESCE(COUNT(y.timestamp), 0) AS cnt
        FROM (SELECT DATE_FORMAT(DATE_ADD('2010-01-01', INTERVAL n.id - 1 SECOND), '%T') AS ts
                FROM numbers n) x
   LEFT JOIN TABLE y ON y.timestamp = x.ts
    GROUP BY x.ts