创建多个OracleConnection对象连接不同的数据库:
OracleConnection oraConnDB_A = new OracleConnection("a");
OracleConnection oraConnDB_B = new OracleConnection("b");
OracleCommand oracleComm = new OracleCommand("select * from a", oraConnDB_A);
oracleComm = new OracleCommand("select * from b", oraConnDB_B);