[Ildar-tsr]

Код:

ADOQuery.SQL.Text:= 'select sum(Summa) s from table_name where Priznak = 1';
If ADOQuery.Active then
  ADOQuery.Close;
ADOQuery.Open;
S:= ADOQuery.FieldByName('s').AsFloat;

если S - integer, то

Код:

S:= ADOQuery.FieldByName('s').AsInteger;