select * from A; //no problem
select * from B; // no problem
select * from A inner join B on B.id = A.bId; // no problem + joining

var cm1 = connection.CreateCommand();
cm1.CommandText = "select * from A;";
var cm2 = connection.CreateCommand();
cm2.CommandText = "select * from B;";
var cm3 = connection.CreateCommand();
cm3.CommandText = "select * from A inner join B on B.id = A.bId;";
...
var dt1 = cm1.ExecuteReader(); // ok
var dt2 = cm2.ExecuteReader(); // ok
var dt3 = cm3.ExecuteReader(); // crash oracle error ORA-00911 : invalid character

cm3.CommandText = "select * from A inner join B on ( B.id = A.bId ) ;";

cm3.CommandType = CommandType.Text;