Hi,

try this one, I hope it will help:

select
  bh.Tank_no, bh.Start_time, bh.End_time,
  ts.Output_Reading - te.Output_Reading as Trend_Tonne,
  eds.Output_Reading - ede.Output_Reading as External_Data_Tonne
from
  Batch_History as bh
  inner join Trend as ts -- Trend start
    on (ts.Tank_no = bh.Tank_no) and (ts.Time_Stamp = bh.Start_time)
  inner join Trend as te -- Trend end
    on (te.Tank_no = bh.Tank_no) and (te.Time_Stamp = bh.End_time)
  inner join External_Data as eds -- External data start
    on (eds.Tank_no = eds.Tank_no) and (eds.Time_Stamp = bh.Start_time)
  inner join External_Data as ede -- External data end
    on (ede.Tank_no = bh.Tank_no) and (ede.Time_Stamp = bh.End_time)
order by
  bh.Tank_no

By the way, is the example incorrect ? Shouldn't the Output_Reaging value for Start_Time (12/21/2004 2:56:45 PM) be 105 instead of 107 ?

Regards,

Goce.