data67 has asked for the wisdom of the Perl Monks concerning the following question:

HI all, I have been trying to figuare out a way to fix a problem that i have been having in my perl code. The issue is that i have to make a call to the table and check for the existance of overlapping dates before i insert a row in my table.

I know some people will suggest "Date::Calc" etc but i wanted to somehow just do this check in my sql call and save time (instead of reading each row and running a date::calc on it). how can i do this? is there a simpler way to do a range check? (maybe with SQL and/or/between? I think between wont work because i have to check 2 dates against 2 params in my program? i donno?)

I want to check that there is no overlapping row in the table where the effective date & expiration date overlap. think of this like a scheduling system where i cant book an appointment over another. here is what my table look like: 

Table: Company_relationship

company_number
relationship_type
effective_date
expiration_date

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Re: Overlapping dates Issue
by ikegami (Patriarch) on Mar 20, 2006 at 22:43 UTC

    If there is no range (just single dates), that's easy. Just count the rows: 

    SELECT COUNT(*)
  FROM Company_relationship
 WHERE effective_date  = ?
    OR expiration_date = ?

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    If effective_date and expiration_date are begin and end dates, I bet you can do: 

    SELECT COUNT(*)
  FROM Company_relationship
 WHERE effective_date <= ?
   AND expiration_date > ?

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    Both return one record with one field. If it's 0, proceed. Otherwise, you have an overlap.

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      Actually, yes there is a concept here of overlapping. I used your query and it did not work for all cases. I went on Oracles website and found the answer there. Here is the link:

      http://asktom.oracle.com/pls/ask/f?p=4950:8:15236886734525876868::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:4921012347969,

      and we said... Do you need to be concerned with all overlaps? Eg: in database you have

      01-jan-2001 07-jan-2001

      you are given as inputs: 

        15-dec-2000     15-jan-2001   - wider then database
  15-dec-2000     04-jan-2001   - overlaps but not contained within
  04-jan-2001     15-jan-2001   - overlaps but not contained within
  02-jan-2001     04-jan-2001   - overlaps and contained within

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      should all four return a "hit"? 

      select *
  from t
  where ( c_beginning between p_beginning and p_ending      -- rule 1
       OR c_ending between p_beginning and p_ending         -- rule 2
       OR ( c_beginning < p_beginning and p_ending < c_ending ) );  --
+ rule 3

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      will do that. If you use the following "chart", it depicts all of the possibles and which "rule" in the predicate above will catch them: 
      .............................................
             CB                CE
PB                                     PE     -- rule 1
PB                   PE                       -- rule 1
                     PB                PE     -- rule 2
                  PB     PE                   -- rule 3
PB  PE                                        -- no hit
                                        PB PE -- no hit

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      Thanks,
      data

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