sql server - Date Exists between Range of Dates not working -

alter procedure [dbo].[spinsert] (@planname varchar(50)=null ,@startdate datetime ,@enddate datetime ,@modifiedby varchar(100)=null ,@returnvalue int out) begin if not exists(select planname dbo.tblplan planname=@planname)  begin  if((select count(*) tblplan startdate <= @startdate  , enddate <=     @enddate)<0)  begin  insert dbo.tblplan values(3,@planname,@startdate,@enddate,@modifiedby,getdate(),         (select datediff(dd,@startdate,@enddate)))  set @returnvalue=1;  end else set @returnvalue=-2; end else set @returnvalue=-1; end 

i trying achieve below thing.i want check user supplied startdate , enddate in between existing table startdate , enddate. if of date of user supplied date range in between tables start date , end date,it should return -2,if record not exists should insert details..

i not achieve logic.where went wrong ..please suggest me solution this.

edit:first consditon check whether planname exists or not,if not exists want check start , end date existed or not(including start , end) tried 2 ways suggested mentioned in replies.

eg:if existing start , end range start-2013-10-09,end-2013-10-15,if going insert plan start , end date of plan should not fall between 9th-15th october , start , end date should not 9th or 15 th both.

one:if((select count(*) tblplan startdate <= @startdate  , enddate <=    @enddate)=0)   result: not insert data, out of previous date. or in  range   second:if((select count(*) tblplan startdate>=@startdate ,    enddate<=@enddate)=0)   result: insert date out considering above condition. 

i think need change if from

if((select count(*) tblplan startdate <= @startdate  , enddate <= @enddate)<0) 

to

if((select count(*) tblplan startdate <= @startdate  , enddate >= @enddate)=0) 

which should ensure @startdate , @enddate between startdate , enddate , test =0