sybase ase - sql compute difference between 2 rows -

i'm looking methodology compare difference between 2 rows in same table. found here (how difference between 2 rows column field?) it's wanted. have done following code:

create table #tmptest (     id_fund int null,     id_sharetype int null,     valuedate datetime null,     varnav float null,     fundperf float null, )  insert #tmptest(id_fund, id_sharetype, valuedate, varnav) values(1,1,'20140101',100) insert #tmptest(id_fund, id_sharetype, valuedate, varnav)  values(1,1,'20140102',20)  update #tmptest set hrc.fundperf = (isnull(hrn.varnav, 0) - hrc.varnav)/hrc.varnav #tmptest hrc  left join #tmptest hrn on hrn.valuedate = (select min(valuedate) #tmptest valuedate > hrc.valuedate) , hrc.id_fund = hrn.id_fund , hrc.id_sharetype = hrn.id_sharetype  

my issue result i'm computing starts on line 1 instead of line 2.

hereunder result i'm obtaining:

id_fund id_sharetype valuedate           varnav                       fundperf                      ------- ------------ ------------------- ------- -----------------------------       1            1 2014-01-01 00:00:00     100                          -0.8       1            1 2014-01-02 00:00:00      20                            -1 

whereas i'd way:

id_fund id_sharetype valuedate           varnav                       fundperf                      ------- ------------ ------------------- ------- -----------------------------       1            1 2014-01-01 00:00:00     100                            -1       1            1 2014-01-02 00:00:00      20                          -0.8 

what's wrong approach?

you not restricting minimum same fund , share type.

update #tmptest     set hrc.fundperf = (isnull(hrn.varnav, 0) - hrc.varnav)/hrc.varnav     #tmptest hrc left join          #tmptest hrn          on hrn.valuedate = (select min(valuedate)                              #tmptest tt                              tt.valuedate > hrc.valuedate ,                                    hrc.id_fund = tt.id_fund , hrc.id_sharetype = tt.id_sharetype                              ) ,            hrc.id_fund = hrn.id_fund , hrc.id_sharetype = hrn.id_sharetype ;