Best way to create on the fly, date ranges, for use with report.
So I can avoid empty rows on my report if there's no activity for a given day.
Mostly to avoid this issue: http://stackoverflow.com/questions/75752/what-is-the-most-straightforward-way-to-pad-empty-dates-in-sql-results-on-either
My advice is: don't make your life harder, make it easier. Just create a table with one row for each calendar day, having as many rows as you think you reasonably need to last. In datawarehousing, this is the common solution, and it is so widely implemented this way that a dwh that doesn't have it, has a code smell.
Many people used to dealing with more traditional oltp/data entry apps feel a natural revulsion against this idea, because the feel the can generate the data anyway, and therefore it shouldn't be stored. But if you do create a table like that, you can adorn it with many useful attributes, such as whether it's a holdiday or a weekend, and you can store many common date representations (iso, european, us format etc) inside it, which can save you a ton of time when creating reports (since you don't have to bother figuring out how the date formatting works in each reporting tool you come by. Or you can go a step further and update your date table everyday to mark flags for the current day, current week, current month, current year, etc - all kinds of useful tools that make it much, much easier to build reports that need to work against some date range.
MySQL sample code as per request in comment:
delimiter //
DROP PROCEDURE IF EXISTS p_load_dim_date
//
CREATE PROCEDURE p_load_dim_date (
p_from_date DATE
, p_to_date DATE
)
BEGIN
DECLARE v_date DATE DEFAULT p_from_date;
DECLARE v_month tinyint;
CREATE TABLE IF NOT EXISTS dim_date (
date_key int primary key
, date_value date
, date_iso char(10)
, year smallint
, quarter tinyint
, quarter_name char(2)
, month tinyint
, month_name varchar(10)
, month_abbreviation varchar(10)
, week char(2)
, day_of_month tinyint
, day_of_year smallint
, day_of_week smallint
, day_name varchar(10)
, day_abbreviation varchar(10)
, is_weekend tinyint
, is_weekday tinyint
, is_today tinyint
, is_yesterday tinyint
, is_this_week tinyint
, is_last_week tinyint
, is_this_month tinyint
, is_last_month tinyint
, is_this_year tinyint
, is_last_year tinyint
);
WHILE v_date < p_to_date DO
SET v_month := month(v_date);
INSERT INTO dim_date(
date_key
, date_value
, date_iso
, year
, quarter
, quarter_name
, month
, month_name
, month_abbreviation
, week
, day_of_month
, day_of_year
, day_of_week
, day_name
, day_abbreviation
, is_weekend
, is_weekday
) VALUES (
v_date + 0
, v_date
, DATE_FORMAT(v_date, '%y-%c-%d')
, year(v_date)
, ((v_month - 1) DIV 3) + 1
, CONCAT('Q', ((v_month - 1) DIV 3) + 1)
, v_month
, DATE_FORMAT(v_date, '%M')
, DATE_FORMAT(v_date, '%b')
, DATE_FORMAT(v_date, '%u')
, DATE_FORMAT(v_date, '%d')
, DATE_FORMAT(v_date, '%j')
, DATE_FORMAT(v_date, '%w') + 1
, DATE_FORMAT(v_date, '%W')
, DATE_FORMAT(v_date, '%a')
, IF(DATE_FORMAT(v_date, '%w') IN (0,6), 1, 0)
, IF(DATE_FORMAT(v_date, '%w') IN (0,6), 0, 1)
);
SET v_date := v_date + INTERVAL 1 DAY;
END WHILE;
CALL p_update_dim_date();
END;
//
DROP PROCEDURE IF EXISTS p_update_dim_date;
//
CREATE PROCEDURE p_update_dim_date()
UPDATE dim_date
SET is_today = IF(date_value = current_date, 1, 0)
, is_yesterday = IF(date_value = current_date - INTERVAL 1 DAY, 1, 0)
, is_this_week = IF(year = year(current_date) AND week = DATE_FORMAT(current_date, '%u'), 1, 0)
, is_last_week = IF(year = year(current_date - INTERVAL 7 DAY) AND week = DATE_FORMAT(current_date - INTERVAL 7 DAY, '%u'), 1, 0)
, is_this_month = IF(year = year(current_date) AND month = month(current_date), 1, 0)
, is_last_month = IF(year = year(current_date - INTERVAL 1 MONTH) AND month = month(current_date - INTERVAL 1 MONTH), 1, 0)
, is_this_year = IF(year = year(current_date), 1, 0)
, is_last_year = IF(year = year(current_date - INTERVAL 1 YEAR), 1, 0)
WHERE is_today
OR is_yesterday
OR is_this_week
OR is_last_week
OR is_this_month
OR is_last_month
OR is_this_year
OR is_last_year
OR IF(date_value = current_date, 1, 0)
OR IF(date_value = current_date - INTERVAL 1 DAY, 1, 0)
OR IF(year = year(current_date) AND week = DATE_FORMAT(current_date, '%u'), 1, 0)
OR IF(year = year(current_date - INTERVAL 7 DAY) AND week = DATE_FORMAT(current_date - INTERVAL 7 DAY, '%u'), 1, 0)
OR IF(year = year(current_date) AND month = month(current_date), 1, 0)
OR IF(year = year(current_date - INTERVAL 1 MONTH) AND month = month(current_date - INTERVAL 1 MONTH), 1, 0)
OR IF(year = year(current_date), 1, 0)
OR IF(year = year(current_date - INTERVAL 1 YEAR), 1, 0)
;
//
delimiter ;
Using p_load_dim_date you uinitially load the dim_date table with say 25 years of data. And daily, prefereabluy round midnight, you run p_update_dim_date. Then you can use the flag fields is_today, is_yesterday, is_this_week, is_last_week and so on to select common ranges. Of course, you should amend this code to suit your particular needs but this is the idea. So no generaging ranges on the fly, you just preload for a long enough period of time ahead. For the time of day, a similar design can be set up - you should be able to manage that yourself going by this code.
For even fancier date dimensions that take care of holidays, and localized names for month and days, you can take a look at: http://rpbouman.blogspot.com/2007/04/kettle-tip-using-java-locales-for-date.html and http://rpbouman.blogspot.com/2010/01/easter-eggs-for-mysql-and-kettle.html
There is no straightforward way to do that in MySQL. Your best bet is to generate a daterange array in your server-side language of choice, and then pull data from the database and merge the resulting array with your daterange array using the date as a key.
Which server side language are you using?
Edit:
Basically what you would do is (pseudocode):
// Create an array with all dates for a given range
dates = makeRange(startDate, endDate);
getData = mysqlQuery('SELECT date, x, y, z FROM a WHERE a AND b AND c');
while (r = fetchRowArray(getData)) {
dates[ date(r['date']) ] = Array ( x, y, z);
}
You end up with an array of dates you can loop through, with the dates that have or don't have activity data associated to them.
Can easily be modified to group / filter data by hours.