Delphi 组件，但它应该是NULL，而不是生成AV。2013年仍在使用BDE吗？哇……2013年还在使用溴化二苯醚吗？哇！ ` qConsulta2 := TQuery.Create(Application); qConsulta2.DatabaseName :

---

组件，但它应该是

NULL

，而不是生成AV。2013年仍在使用BDE吗？哇……2013年还在使用溴化二苯醚吗？哇！

` qConsulta2 := TQuery.Create(Application);
  qConsulta2.DatabaseName := 'BaseDato';
  qConsulta2.SQL.Text := 'select VALOR from PARAMETRO where codigoPARAMETRO  = ''IVA'' ';
  qConsulta2.open;
  qCompraDetalle.FieldByName('PORCENTAJE_IVA').AsFloat:=        qConsulta2.fieldbyname('valor').asfloat;
  qConsulta2.close;
  qConsulta2.free `

qConsulta2 := TQuery.Create(Application);
try
  qConsulta2.DatabaseName := 'BaseDato';
  qConsulta2.SQL.Text := 'select VALOR from PARAMETRO where codigoPARAMETRO  = ''IVA'' ';
  qConsulta2.open;
  if not qConsulta2.EOF then  
   qCompraDetalle.FieldByName('PORCENTAJE_IVA').AsFloat:= qConsulta2.fieldbyname('valor').asfloat;
  qConsulta2.close;
finally 
  qConsulta2.free 
end;

qConsulta2 := TQuery.Create(Application);
try
  qConsulta2.DatabaseName := 'BaseDato';
  qConsulta2.SQL.Text := 'select COALESCE(VALOR, 0) AS valor from PARAMETRO where codigoPARAMETRO  = ''IVA'' ';
  qConsulta2.open;
  qCompraDetalle.FieldByName('PORCENTAJE_IVA').AsFloat:= qConsulta2.fieldbyname('valor').asfloat;
  qConsulta2.close;
finally 
  qConsulta2.free 
end;

qConsulta2 := TQuery.Create(Application);
try
  qConsulta2.DatabaseName := 'BaseDato';
  qConsulta2.SQL.Text := 'select VALOR from PARAMETRO where codigoPARAMETRO  = ''IVA'' ';
  qConsulta2.open;
  if qConsulta2.FieldByName('VALOR').AsString <> '' then  
   qCompraDetalle.FieldByName('PORCENTAJE_IVA').AsFloat:= qConsulta2.fieldbyname('valor').asfloat;
  qConsulta2.close;
finally 
  qConsulta2.free 
end;

procedure TForm1.Case1;
var
  f : double;
begin
  db.ExecSQL('delete from PARAMETRO');
  db.ExecSQL('insert into PARAMETRO (codigoPARAMETRO) values(''IVT'')');
// VALOR_FLOAT and VALOR_TEXT are null
  qConsulta2.SQL.Text := 'select * from PARAMETRO';
  qConsulta2.Open();
  f := qConsulta2.FieldByName('VALOR_FLOAT').AsFloat;
  ShowMessage('From Float '+FloatToStr(f));
  f := qConsulta2.FieldByName('VALOR_TEXT').AsFloat;
  ShowMessage('From Text '+FloatToStr(f));
end;

procedure TForm1.Case2;
var
  f : double;
begin
  db.ExecSQL('delete from PARAMETRO');
  db.ExecSQL('insert into PARAMETRO (codigoPARAMETRO,VALOR_TEXT) values(''IVT'','''')');
// VALOR_FLOAT is null and VALOR_TEXT is '' (zero length string)
  qConsulta2.SQL.Text := 'select * from PARAMETRO';
  qConsulta2.Open();
  f := qConsulta2.FieldByName('VALOR_FLOAT').AsFloat;
  ShowMessage('From Float '+FloatToStr(f));
  f := qConsulta2.FieldByName('VALOR_TEXT').AsFloat;
  ShowMessage('From Text '+FloatToStr(f));
end;

procedure TForm1.Case3;
var
  f : double;
begin
  NullStrictConvert := false;
  db.ExecSQL('delete from PARAMETRO');
  db.ExecSQL('insert into PARAMETRO (codigoPARAMETRO) values(''IVT'')');
// VALOR_FLOAT and VALOR_TEXT are null
  qConsulta2.SQL.Text := 'select * from PARAMETRO';
  qConsulta2.Open();
  f := qConsulta2.FieldByName('VALOR_FLOAT').AsFloat;
  ShowMessage('From Float '+FloatToStr(f));
  f := qConsulta2.FieldByName('VALOR_TEXT').AsVariant;
  ShowMessage('From Text '+FloatToStr(f));
end;

procedure TForm1.Case4;
var
  f : double;
begin
  NullStrictConvert := false;
  db.ExecSQL('delete from PARAMETRO');
  db.ExecSQL('insert into PARAMETRO (codigoPARAMETRO) values(''IVT'')');
// VALOR_FLOAT and VALOR_TEXT are null
  qConsulta2.SQL.Text := 'select * from PARAMETRO';
  qConsulta2.Open();
  f := qConsulta2['VALOR_FLOAT'];
  ShowMessage('From Float '+FloatToStr(f));
  f := qConsulta2['VALOR_TEXT'];
  ShowMessage('From Text '+FloatToStr(f));
  // avoid data conversion
  qCompraDetalle.Open();
  qCompraDetalle.Append;
  qCompraDetalle['PORCENTAJE_IVA'] := qConsulta2['VALOR_TEXT'];
  qCompraDetalle.Post;
end;