Question

I am struggling with the appropriate query to find duplicates while at the same time respecting the effective start and end dates for the record. Example data below.

ClientName   ClientID   EffectiveStart  EffectiveEnd
A            1          1900-01-01      2100-01-01
A            1          1900-01-01      2100-01-01
B            2          1900-01-01      2012-05-01
C            2          2012-05-01      2100-01-01
D            3          1900-01-01      2012-05-01
E            3          2012-04-30      2100-01-01
F            4          2012-04-15      2100-01-01

The output I am looking for is below.

ClientName  ClientID
A           1
D           3
E           3

The logic is that Client A has ID 1 duplicated. Client B and C have a duplicate (2) BUT the date ranges are such that the two duplicates DO NOT overlap each other, which means they should not be considered duplicates. Client D and E have ID 3 duplicated AND the date ranges overlap so it should be considered a duplicate. Client F does not have a duplicate so should not show in the output.

Any thoughts? Questions?

Answer 1

Will need a PK

select c1.name, c2.name, c1.id
from client c1 
join client c2 on c1.id = c2.id and c1.PK < c2.PK
where c1.Start > c2.End or c1.End < c2.Start

Determine Whether Two Date Ranges Overlap please give him a +1