找出数据库中的某个域最接近给定值的上、下值

//摘自网上
function GetNearValue(tblName,fldName,confldName,confldValue:string; GivenValue:Double;

                      var LowValue, HighValue:Double):Boolean;

var
  s:string;

begin
  Result:=False;
  s:='SELECT Max_V,Min_V FROM '+
     '(SELECT MAX('+fldName+') AS Max_V FROM '+tblName+
     ' WHERE ('+fldName+'<='+ FloatToStr(GivenValue)+') AND ('+confldName+'= '''+confldValue+''')) AS Max_Tbl,'+
     '(SELECT MIN('+fldName+') AS Min_V FROM '+tblName+
     ' WHERE ('+fldName+'>='+ FloatToStr(GivenValue)+') AND ('+confldName+'= '''+confldValue+''')) AS Min_Tbl';
  with frmDM.adoqryTmp do
  begin
    Close;
    SQL.Clear;
    SQL.Add(s);
    try
      Open;
      if RecordCount > 0 then
      begin
        LowValue:=VarToFloat(FieldValues['Min_V']);
        HighValue:=VarToFloat(FieldValues['Max_V']);
        Close;
        Result:=True;
      end;  
    except
      Close;
    end;  
  end;
end;