select * from table1 t1
left join v_table2 t2 on t2.id = t1.id

create or replace view v_table2 
as
select distinct id from table2@schema2

try
{
	connection.Open();
	transaction = connection.BeginTransaction(IsolationLevel.ReadCommitted);//здесь вылетает ORA-01453: оператор SET TRANSACTION должен быть первым в транзакции

}
catch (Exception ex)
{
	throw new BeginTransactionException(ex);
}