Group by function use in sql

Question

I want to get an output using group by function of there is no data in the table to display a particular value
for eg:
SELECT TRUNC(updated_date) DATE1 , COUNT(1) COUNT FROM table
where TRUNC(updated_date) >=TRUNC(SYSDATE-18) AND TRUNC(updated_date) <=TRUNC(SYSDATE)
GROUP BY TRUNC(updated_date)
ORDER BY TRUNC(updated_date) DESC;
DATE1 COUNT
6/16/2012 14208
6/15/2012 307825
6/14/2012 172988
6/6/2012 138790
6/5/2012 167562
6/4/2012 51870
6/2/2012 130582
6/1/2012 239806
But i need the missed out date i.e 6/3/2012 - 0, 6/7/2012 - 0 to be displayed since there is no data on the repective dates.

Answer 1

Hi,
You can only display things that are in a table (or result set, but from now on, I'll just say table), or that can be derived from a table. If you want to display dates that are not in your table, then you have to get them from another table, or derive them from some table.
Some people actually keep tables of possible dates for queries like this. In this case, all you need is a table of the last 19 dates, ending with today. That's easy to derive from dual:
WITH     all_dates     AS
     SELECT     TRUNC (SYSDATE)     - LEVEL     AS date1
     ,     TRUNC (SYSDATE) + 1 - LEVEL     AS date2
     FROM     dual
     CONNECT BY     LEVEL <= 19
SELECT    a.date1
,        COUNT (x.updated_date)     AS count
FROM                all_dates     a
LEFT OUTER JOIN    table_x     x  ON     x.updated_date     >= a.date1
                            AND     x.updated_date     <  a.date2
GROUP BY  a.date1
ORDER BY  a.date1
;If you'd care to post CREATE TABLE and INSERT statements for some sample data, and the results you want from that data, then I could test this.