What is the most straightforward way to pad empty dates in sql results (on either mysql or perl end)?

Question

I\'m building a quick csv from a mysql table with a query like:

select DATE(date),count(date) from table group by DATE(date) order by date asc;

Answer 1

You could use a DateTime object:

use DateTime;
my $dt;

while ( my ($date, $sum) = $sth->fetchrow )  {
    if (defined $dt) {
        print CSV $dt->ymd . ",0\n" while $dt->add(days => 1)->ymd lt $date;
    }
    else {
        my ($y, $m, $d) = split /-/, $date;
        $dt = DateTime->new(year => $y, month => $m, day => $d);
    }
    print CSV, "$date,$sum\n";
}

What the above code does is it keeps the last printed date stored in a DateTime object $dt, and when the current date is more than one day in the future, it increments $dt by one day (and prints it a line to CSV) until it is the same as the current date.

This way you don't need extra tables, and don't need to fetch all your rows in advance.

Answer 2

I hope you will figure out the rest.

select  * from (
select date_add('2003-01-01 00:00:00.000', INTERVAL n5.num*10000+n4.num*1000+n3.num*100+n2.num*10+n1.num DAY ) as date from
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n1,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n2,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n3,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n4,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n5
) a
where date >'2011-01-02 00:00:00.000' and date < NOW()
order by date

With

select n3.num*100+n2.num*10+n1.num as date

you will get a column with numbers from 0 to max(n3)*100+max(n2)*10+max(n1)

Since here we have max n3 as 3, SELECT will return 399, plus 0 -> 400 records (dates in calendar).

You can tune your dynamic calendar by limiting it, for example, from min(date) you have to now().

Answer 3

Use some Perl module to do date calculations, like recommended DateTime or Time::Piece (core from 5.10). Just increment date and print date and 0 until date will match current.