delphi dxExpress MySQL: invalid LAST_INSERT_ID value - mysql

Question

I am developing an application in Delphi and want to insert records to Mysql's table.
An then I want to know inserted record's identity value. So I write bellow code.
On run time , insert is done and record added but returned value for identity is zero!!
what is my mistake ?!!
-- MySql table create
CREATE TABLE Sample_Table (
id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
mobile_number varchar(20) DEFAULT NULL,
message_body text,
PRIMARY KEY (id)
);
--- Delphi code
SQLCon := TSQLConnection.Create(self);
with SQLCon do begin
Close;
DriverName := 'MySQL';
GetDriverFunc := 'getSQLDriverMYSQL';
LibraryName := 'dbxmys.dll';
VendorLib := 'LIBMYSQL.dll';
LoginPrompt := false;
Params.Values['HostName'] := '127.0.0.1';
Params.Values['Database'] := 'sms_test';
Params.Values['User_Name'] := 'root';
Params.Values['Password'] := 'root';
Open;
end;
SQLQry := TSQLQuery.Create(self);
with SQLQry do begin
Close;
SQLConnection := SQLCon;
SQL.Clear;
SQL.Add('INSERT INTO Sample_Table ');
SQL.Add('(mobile_number, message_body) VALUES');
SQL.Add(format('(%s, %s);',[QuotedStr('989121011689'), QuotedStr('Text1')]));
ExecSQL();
Close;
SQL.Clear;
SQL.Add('SELECT LAST_INSERT_ID() EngineRefNo;');
Open;
First;
ListBox1.items.Add(FieldByName('EngineRefNo').AsString);
Close;
end;
SQLCon.Close;
any advise?

Answer 1

You should get the ID in one go
SQLQry := TSQLQuery.Create(self);
with SQLQry do begin
SQLConnection := SQLCon;
SQL.Add('INSERT INTO Sample_Table ');
SQL.Add('(mobile_number, message_body) VALUES');
SQL.Add(format('(%s, %s);',[QuotedStr('989121011689'), QuotedStr('Text1')]));
SQL.Add('SELECT LAST_INSERT_ID() EngineRefNo;');
Open;
ListBox1.items.Add(FieldByName('EngineRefNo').AsString);
Close;
end;
SQLCon.Close;
and you should think about using parameters to prevent sql injection
SQLQry := TSQLQuery.Create(self);
with SQLQry do begin
SQLConnection := SQLCon;
SQL.Add('INSERT INTO Sample_Table ');
SQL.Add('( mobile_number, message_body ) VALUES');
SQL.Add('( :mobile_number, :message_body );');
SQL.Add('SELECT LAST_INSERT_ID() EngineRefNo;');
ParamByName( 'mobile_number' ).Value := '989121011689';
ParamByName( 'message_body' ).Value := 'Text1';
Open;
ListBox1.items.Add(FieldByName('EngineRefNo').AsString);
Close;
end;
SQLCon.Close;

Answer 2

Apparently this is a problem known with delphi .
quoting the above link:
Certain ODBC applications (including Delphi and Access) may have
trouble obtaining the auto-increment value using the previous
examples. In this case, try the following statement as an alternative:
SELECT * FROM tbl WHERE auto IS NULL;
This alternative method requires that sql_auto_is_null variable is not
set to 0. See Server System Variables
So in your case (untested):
SQLCon := TSQLConnection.Create(self);
with SQLCon do begin
Close;
DriverName := 'MySQL';
GetDriverFunc := 'getSQLDriverMYSQL';
LibraryName := 'dbxmys.dll';
VendorLib := 'LIBMYSQL.dll';
LoginPrompt := false;
Params.Values['HostName'] := '127.0.0.1';
Params.Values['Database'] := 'sms_test';
Params.Values['User_Name'] := 'root';
Params.Values['Password'] := 'root';
Open;
end;
SQLQry := TSQLQuery.Create(self);
with SQLQry do begin
Close;
SQLConnection := SQLCon;
SQL.Clear;
SQL.Add('INSERT INTO Sample_Table ');
SQL.Add('(mobile_number, message_body) VALUES');
SQL.Add(format('(%s, %s);',[QuotedStr('989121011689'), QuotedStr('Text1')]));
ExecSQL();
Close;
SQL.Clear;
SQL.Add('SELECT id FROM Sample_Table WHERE id IS NULL');
Open;
First;
ListBox1.items.Add(FieldByName('Id').AsString);
Close;
end;
SQLCon.Close;