LINQ

select a.LoanNum, PromiseAmt, isnull(SUM(PdAmt), 0) as PostedAmt
 from LoanPromises a with(nolock)
 left outer join LoanPayment lp with(nolock) on a.LoanNum = lp.LoanNum and a.PromiseDt < lp.PmtPostDt
 group by a.LoanNum, PromiseAmt
 having isnull(Sum(PdAmt),0) < PromiseAmt
 
Here is my linq query
 
var query = from pmts in oLoan.LoanPayments
     join promise in oLoan.LoanPromiseToPays
    on new { p1 = pmts.LoanNum, p2 = pmts.PmtPostDt} equals new {LoanNum = promise.LoanNum, PmtPostDt = promise.PromiseDt } into outer
 from defaulted in outer.DefaultIfEmpty()
 group defaulted by promise.LoanNum && promise.PromiseAmt into grouped
 select new
 {
    LoanNum = grouped.Key,
    Sum = grouped.Sum(t => t.PdAmt < t.PromiseAmt),
    PmtPostDt = promise.PromiseDt ?? default(DateTime)
 }