title: SQL query does not update table
body: <p>I have got an <code>UPDATE</code> query, what works well when I execute it in MS Managment Studio.
  But if I try execute this query from my c# app, it executes without any exceptions, but does not update the table. Connection string is right.
  This is the way I do it:</p>
  
  <pre><code>int contractId = 2
  con.ConnectionString = @"Data Source=(LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\tst.mdf;Integrated Security=True;Connect Timeout=30";
  con.Open();
  SqlCommand cmd = con.CreateCommand();
  cmd.CommandText = "update аренды set datetime_возврата=GETDATE() where id_договора=@contractId";
  cmd.Parameters.Add("@contract_id", SqlDbType.Int, 4).Value = contractId;         
  cmd.ExecuteNonQuery();
  </code></pre>
  
  <p>What can be wrong?</p>