How to fill missing dates by groups in a table in sql - sql

Question

I want to know how to use loops to fill in missing dates with value zero based on the start/end dates by groups in sql so that i have consecutive time series in each group. I have two questions.
how to loop for each group?
How to use start/end dates for each group to dynamically fill in missing dates?
My input and expected output are listed as below.
Input: I have a table A like
date value grp_no
8/06/12 1 1
8/08/12 1 1
8/09/12 0 1
8/07/12 2 2
8/08/12 1 2
8/12/12 3 2
Also I have a table B which can be used to left join with A to fill in missing dates.
date
...
8/05/12
8/06/12
8/07/12
8/08/12
8/09/12
8/10/12
8/11/12
8/12/12
8/13/12
...
How can I use A and B to generate the following output in sql?
Output:
date value grp_no
8/06/12 1 1
8/07/12 0 1
8/08/12 1 1
8/09/12 0 1
8/07/12 2 2
8/08/12 1 2
8/09/12 0 2
8/10/12 0 2
8/11/12 0 2
8/12/12 3 2
Please send me your code and suggestion. Thank you so much in advance!!!

Answer 1

You can do it like this without loops
SELECT p.date, COALESCE(a.value, 0) value, p.grp_no
FROM
(
SELECT grp_no, date
FROM
(
SELECT grp_no, MIN(date) min_date, MAX(date) max_date
FROM tableA
GROUP BY grp_no
) q CROSS JOIN tableb b
WHERE b.date BETWEEN q.min_date AND q.max_date
) p LEFT JOIN TableA a
ON p.grp_no = a.grp_no
AND p.date = a.date
The innermost subquery grabs min and max dates per group. Then cross join with TableB produces all possible dates within the min-max range per group. And finally outer select uses outer join with TableA and fills value column with 0 for dates that are missing in TableA.
Output:
| DATE | VALUE | GRP_NO |
|------------|-------|--------|
| 2012-08-06 | 1 | 1 |
| 2012-08-07 | 0 | 1 |
| 2012-08-08 | 1 | 1 |
| 2012-08-09 | 0 | 1 |
| 2012-08-07 | 2 | 2 |
| 2012-08-08 | 1 | 2 |
| 2012-08-09 | 0 | 2 |
| 2012-08-10 | 0 | 2 |
| 2012-08-11 | 0 | 2 |
| 2012-08-12 | 3 | 2 |
Here is SQLFiddle demo

Answer 2

I just needed the query to return all the dates in the period I wanted. Without the joins. Thought I'd share for those wanting to put them in your query. Just change the 365 to whatever timeframe you are wanting.
DECLARE #s DATE = GETDATE()-365, #e DATE = GETDATE();
SELECT TOP (DATEDIFF(DAY, #s, #e)+1)
DATEADD(DAY, ROW_NUMBER() OVER (ORDER BY number)-1, #s)
FROM [master].dbo.spt_values
WHERE [type] = N'P' ORDER BY number

Answer 3

The following query does a union with tableA and tableB. It then uses group by to merge the rows from tableA and tableB so that all of the dates from tableB are in the result. If a date is not in tableA, then the row has 0 for value and grp_no. Otherwise, the row has the actual values for value and grp_no.
select
dat,
sum(val),
sum(grp)
from
(
select
date as dat,
value as val,
grp_no as grp
from
tableA
union
select
date,
0,
0
from
tableB
where
date >= date '2012-08-06' and
date <= date '2012-08-13'
)
group by
dat
order by
dat
I find this query to be easier for me to understand. It also runs faster. It takes 16 seconds whereas a similar right join query takes 32 seconds.
This solution only works with numerical data.
This solution assumes a fixed date range. With some extra work this query can be adapted to limit the date range to what is found in tableA.