sql server - TSQL check constraint related to existing rows -


i have following table:

create table dbo.mytable]  (     id1 [int] not null,     id2 [int] not null,     startdate smalldatetime not null,     enddate smalldatetime null,     constraint [pk_mytable1] primary key clustered (id1 asc, id2 asc, startdate asc) ) on [primary]

i want ensure startdate enddate period each id1 , id2 unique, , there no overlap.

how create check constraint this:

(     id1 <> existingrow.id1     or id2 <> existingrow.id2 ) or (     id1 = existingrow.id1     , id2 = existingrow.id2     , (         startdate >= isnull(existingrow.enddate, startdate + 1)         or isnull(enddate, existingrow.startdate + 1) <= existingrow.startdate     ) )

...or constraint condition this:

if id1 = existingrow.id1 , id2 = existingrow.id2 check (     startdate >= isnull(existingrow.enddate, startdate + 1)     or isnull(enddate, existingrow.startdate + 1) <= existingrow.startdate )

thanks in advance...

did try this?

create function dbo.fn_check_unique_value  (     @id1 int,     @id2 int,     @startdate smalldatetime,     @enddate smalldatetime ) returns int begin     declare @result int      set @result = (select count(*)                       dbo.mytable existingrow                     (   @id1 <> existingrow.id1                              or @id2 <> existingrow.id2                             )                             or (                                 @id1 = existingrow.id1                                 , @id2 = existingrow.id2                                 , (                                      @startdate >= isnull(existingrow.enddate, @startdate + 1)                                      or isnull(@enddate, existingrow.startdate + 1) <= existingrow.startdate                                     )                                ))      return @result end go  alter table dbo.mytable add constraint ck_no_overlap     check ( dbo.fn_check_unique_value(id1, id2, startdate, enddate) <= 1           )

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