C# 每个派生表都必须有自己的别名？

可能重复：

我有两个MYSQL表，它们具有相同的列，我正在尝试获取sum qtd，其中produto相同，但我有一个错误“每个派生表都必须有自己的别名”plz帮助

MySqlCommand cmd = cnn.CreateCommand();
                    StringBuilder query = new StringBuilder();
                    query.Append("select produto,sum(qtd) from ( ");
                    query.AppendFormat(" select x.produto,x.qtd from itens_venda x where x.data='{0:MM/dd/yyyy}'", new object[] { data1 });
                    query.Append(" Union all ");
                    query.AppendFormat(" select y.produto,y.qtd from itens_venda_fiscal y where y.data='{0:MM/dd/yyyy}'", new object[] { data1 });
                    query.Append(" )  group by produto order by sum(qtd) desc  ");
                    cmd.CommandText = query.ToString();
                    MySqlDataReader reader = cmd.ExecuteReader();
                    while ( reader.Read() )
                    {
                        Codigo.Add(reader.GetString(0));
                        Quantidade.Add(reader.GetString(1));
                    }

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是的，每个派生表都必须有自己的别名。添加别名，如下所示

query.Append(" ) as t group by produto order by sum(qtd) desc  ");