Fill missing values with 0 - sql query - mysql

Question

I have an SQL query as outlined below that selects data between two dates.
SELECT date, total FROM db WHERE date >= '2016-03-14' AND date <= '2016-03-20';
I'd like to output a "0" where there's no data for various dates, for example:
Query spans = 2016-03-14 to 2016-03-20
Currently my SQL would output:
Date Total
2016-03-14 50
I'd like to output:
Date Total
2016-03-14 50
2016-03-15 0
2016-03-16 0
2016-03-17 0
2016-03-18 0
2016-03-19 0
2016-03-20 0
Is there any way to do this without complex joins?
Thanks,
Matt

Answer 1

The best way to create records for dates that don't exist in your data is to join to a calendar table.
SELECT a.cal_dt, COALESCE(b.total,0) AS total
FROM lkp_Calendar a
LEFT JOIN db b
ON b.date = a.cal_dt
WHERE a.cal_dt >= '2016-03-14'
AND a.cal_dt <= '2016-03-20';
There are many good scripts out there to create robust calendar tables, a simple one is:
CREATE TABLE lkp_Calendar (cal_dt date);
CREATE PROCEDURE addDates(dateStart DATE, dateEnd DATE)
BEGIN
WHILE dateStart <= dateEnd DO
INSERT INTO lkp_Calendar (cal_dt) VALUES (dateStart);
SET dateStart = date_add(dateStart, INTERVAL 1 DAY);
END WHILE;
END;
CALL addDates('2016-01-01','2016-12-31');

Answer 2

SELECT date, COUNT(*) AS total FROM db WHERE date >= '2016-03-14' AND date <= '2016-03-20' GROUP BY date;
I assume:
date is just a date (has no time part)
total IS NOT a column, just a register count

Answer 3

It doesn't require complex joins. But it does require a rowsource for the missing date values you want returned.
One option is to use a calendar table populated with dates.
create table cal (dt DATE NOT NULL PRIMARY KEY) ... ;
insert into cal (dt) values ('2016-03-01');
insert into cal (dt) select dt + interval 1 day from cal order by dt;
insert into cal (dt) select dt + interval 2 day from cal order by dt;
insert into cal (dt) select dt + interval 4 day from cal order by dt;
insert into cal (dt) select dt + interval 8 day from cal order by dt;
insert into cal (dt) select dt + interval 16 day from cal order by dt;
Then pull the dates from that:
SELECT c.dt
FROM cal c
WHERE c.dt >= '2016-03-14'
AND c.dt < '2016-03-21'
Then just do the simple outer join to your table:
SELECT c.dt AS `date`
, IFNULL(d.total,0) AS `total`
FROM cal c
LEFT
JOIN db d
ON d.date = c.dt
WHERE c.dt >= '2016-03-14'
AND c.dt < '2016-03-21'
ORDER BY c.dt
If you don't have a calendar table, you can use an inline view that does UNION ALL
SELECT c.dt AS `date`
, IFNULL(d.total,0) AS `total`
FROM ( SELECT '2016-03-14' + INTERVAL 0 DAY AS dt
UNION ALL SELECT '2016-03-15' + INTERVAL 0 DAY
UNION ALL SELECT '2016-03-16' + INTERVAL 0 DAY
UNION ALL SELECT '2016-03-17' + INTERVAL 0 DAY
UNION ALL SELECT '2016-03-18' + INTERVAL 0 DAY
UNION ALL SELECT '2016-03-19' + INTERVAL 0 DAY
UNION ALL SELECT '2016-03-20' + INTERVAL 0 DAY
) c
LEFT
JOIN db d
ON d.date = c.dt
ORDER BY c.dt

Answer 4

You can also try the below query. This caters for the scenario where you don't have records for all the dates in the underlying table.
DECLARE #temp TABLE (dbdate DATE, total INT)
DECLARE #StartDate DATE = '2016-03-14'
DECLARE #EndDate DATE = '2016-03-20'
WHILE (#StartDate <= #EndDate)
BEGIN
INSERT #temp
SELECT #StartDate AS [dbDate], ISNULL((SELECT total FROM db WHERE [date] = #StartDate),0) AS Total
SET #StartDate = DATEADD(dd,1,#StartDate)
END
SELECT * FROM #temp

Answer 5

Try this (The fiddle demo is slightly different as I didn't have data of db table)
SQLFiddle Demo
select selected_date,coalesce(count1,0) as count1 from
(select * from
(select adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) selected_date from
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3,
(select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) v
where selected_date between '2016-03-14' and '2016-03-20'
) t
left join
(SELECT dt, count1 FROM db WHERE dt between '2016-03-14' and '2016-03-20') t1
on t.selected_date=t1.dt