Date Periods Overlapping

I found this sitting in drafts, short post regarding period overlapping. With simple logic we can eliminate the OR conditions related to all possible combinations.

The post:

The possible four cases where period overlap can occur are:

case 1:

   A----------B
--------|------------|---------
        C            D
case 2:

                A----------B
--------|------------|---------
        C            D
case 3:

     A-----------------B
--------|-----------|---------
        C           D
case 4:

          A-------B
--------|-----------|---------
        C           D

One way we can determine the overlapping periods is if we use OR conditions for all cases, e.g.:

(start_date_C between start_date_A and end_date_B) -- cases 1,3
OR
(end_date_D between start_date_A and end_date_B) -- cases 2,3
OR
(start_date_A between start_date_C and start_date_D) -- case 4
 

If you are familiar with De Morgan’s laws (from school 🙂 ) then:

“not (A and B)” is the same as “(not A) or (not B)”
also,
“not (A or B)” is the same as “(not A) and (not B)”.

With this implemented, we can get the following condition:

(start_date_A <= end_date_D AND end_date_B >= start_date_C)