Selecting Missing Days from a given range of Date from a table

Question

Dear Oracle Guru's
Consider the following table
txndetails
Rundate date
Txncnt Number
userid varchar2(100)
Data will be as follows
Rundate txncnt userid
17-Nov-2009 4 admin
18-Nov-2009 7 admin
21-Nov-2009 3 admin
23-Nov-2009 4 admin
We populate this table on the basis of txn generated. This is supposed to run daily based on the transactions. Certain days there wont be any transaction at all. hence there will be no entry on this table .
At any given point of time , we would like to know the days on which there is no entries in this table
In the above sample data, there is no entries on 19th, 20th and 22nd
we have to list out those days
I got confused while trying some methods
Kindly guide me in this regard
with warm regards
Ssr

Answer 1

Hi,
As Centinul and Bhushan said, you need a list of all the possible dates; "CONNECT BY LEVEL <= x" is an efficient way to generate such a list in Oracle SQL.
Once you have the list of all days, you can use MINUS, like Centinul or Bhushan did. You can also use an outer join, as shown below.
WITH  extrema     AS
     SELECT     TRUNC (MIN (rundate))     AS start_date
     ,     TRUNC (MAX (rundate))     AS end_date
     FROM     txndetails
all_days     AS
     SELECT     start_date + LEVEL - 1     AS a_date
     ,     start_date + LEVEL        AS next_date
     FROM     extrema
     CONNECT BY     LEVEL <= 1 + end_date - start_date
SELECT     a.a_date
FROM          all_days     a
LEFT OUTER JOIN     txndetails     t     ON     t.rundate >= a.a_date
                                 AND     t.rundate <  a.next_date
WHERE   t.rundate     IS NULL
;Remember that all DATEs include hours, minutes and seconds. In the list of all days that you generate, the hours, minutes and seconds will probably be 00:00:00; be careful if the hours, minutes and seconds in your actual DATEs are not always 00:00:00.
The query above shows missing dates between the first date that is actually in the table and the last date in the table.
In practice, most people are interested in a deffierent range, such as all dates between two given parameters, or all dates within the last year.
If that's the case, you don't need the sub-query extrema; you can use the paremters (or compute the values) in all_days, based on dual.
For example, to get the most recent 365 days:
WITH     all_days     AS
     SELECT     TRUNC (SYSDATE) + LEVEL - 365     AS a_date
     ,     TRUNC (SYSDATE) + LEVEL - 364       AS next_date
     FROM     dual
     CONNECT BY     LEVEL <= 365
SELECT     a.a_date
...          -- Same as beforeEdited by: Frank Kulash on Nov 23, 2009 10:54 AM