How to fill missing dates by groups in a table in

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.

1. how to loop for each group?
2. 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