How to get count for missing month

Question

I created a view as follows:
CREATE OR REPLACE FORCE VIEW "Vinfection1" ("MONTH", "COUNT") AS
select "MONTH","COUNT" from (
select to_char(s.pdate,'Mon-yyyy') as month, count(*) as count
from surproc s, diagnosis_surproc d
where s.surprocid = d.surprocid and d.diagnosisid in ('506', '507', '508', '509', '510')
group by to_char(pdate,'Mon-yyyy'))
order by to_date(month,'Mon-yyyy')
Some months are missing in the view. I want to put that month and 0 in the view. How to do it?
Thanks,
Jennifer

Answer 1

Hi, Jennifer,
You need to outer-join to some table or result set (such as all_months, below) that has one roe per month.
Here's one way:
CREATE OR REPLACE FORCE VIEW Vinfection1 (month, month_s, cnt) AS
WITH    all_months     AS
     SELECT  ADD_MONTHS (first_month, LEVEL - 1)     AS month
     FROM     (
              SELECT  TRUNC (MIN (pdate), 'MONTH')     AS first_month
              ,         TRUNC (MAX (pdate), 'MONTH')     AS last_month
              FROM    surproc
     CONNECT BY     LEVEL <= 1 + MONTHS_NETWEEN (last_month, first_month)
SELECT  a.month
,     TO_CHAR (a.month, 'Mon-yyyy')     AS month_s
,     COUNT (*)                 AS cnt
FROM              all_months      a
LEFT OUTER JOIN      (     surproc               s
               JOIN   diagnosis_surproc      d  ON   s.surprocid     = d.surprocid
                                      AND  d.diagnosisid     IN ('506', '507', '508', '509', '510')
           )     ON  a.month     = TRUNC (s.pdate)
GROUP BY  a.month
/Avoid table- and column names that are non-standatrd (such as names that need double-quotes), or are built-in function names (such as COUNT).
Don't use ORDER BY in a view. Almost anything you do with the view will cause the ordering to be lost anyway.
Even if you do have an ORDER BY clause in the view, you'll often want to ORDER BY month. Rather than call TO_DATE whenever you need to sort, I suggest having two month columns; month (whcih is a DATE) for sorting, filtering and joining, and month_s (whcih is a VARCHAR2) for displaying.
Use ANSI join syntax, especiallly for outer joins.
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all tables involved, and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
Always say which version of Oracle you're using.
Edited by: Frank Kulash on Mar 20, 2012 12:03 PM
Added outer join condition