c# - 是否有比我现在正在做的更有效的方法从 5 个表中获取数据？

Question

所以我想做的是使用 C# 将累积数据放在 ListView 对象上，然后获取销售报告的销售记录。如您所见，它非常不稳定，我的代码就是这样，我主要想删除必须调用两个 MySqlCommands 和 DataReaders 的情况。任何建议将不胜感激!

string query = "SELECT * FROM orderlist ol "+
               "INNER JOIN orderdb o "+
               "ON ol.order_ID = o.order_ID "+
               "INNER JOIN menudb m "+
               "ON ol.menu_ID = m.menu_ID "+   
               "WHERE o.order_date >= '"+fromdate.Date()+"' AND "+
                     "o.order_date <= '"+todate.Date()+"'";
command = new MySqlCommand(query, connection);
dr = command.ExecuteReader();
string[] info = new string[15];
while(dr.Read())
{
  string query2 = "SELECT r.*, s.stock_pricePerPiece FROM recipelist r "+
                  "INNER JOIN stocksdb s ON r.stock_ID = s.stock_ID "+
                  "WHERE r.menu_ID = '"+(dr["menu_ID"].ToString())+"'";
  MySqlCommand cmd2 = new MySqlCommand(query2, connection2);
  MySqlDataReader dr2 = cmd2.ExecuteReader();
  double menu_cost = 0;
  while(dr2.Read())
  {
      menu_cost += Convert.ToDouble(dr2["stock_pricePerPiece"].ToString());
  }

info[1] = (dr["order_ID"].ToString());
info[2] = (dr["order_date"].ToString());
info[3] = (dr["menu_name"].ToString());
info[4] = (menu_cost.ToString("#0.00"));
info[5] = (dr["menu_price"].ToString());
info[6] = (Convert.ToDouble(info[5]) - menu_cost).ToString("#0.00");
this.ReportList.Items.Add(new ListViewItem(new string[] { info[1] , info[2] , info[3] , info[4] , info[5] , info[6] }));
}

Answer 1

是的，您可以在一个查询中执行此操作。您可以像这样加入它们:

SELECT 
  r.* 
FROM  orderlist ol 
INNER JOIN orderdb    o ON ol.order_ID = o.order_ID
INNER JOIN menudb     m ON ol.menu_ID  = m.menu_ID
INNER JOIN recipelist r ON r.menu_ID   = m.menu_ID
INNER JOIN stocksdb   s ON r.stock_ID  = s.stock_ID 
WHERE o.order_date >= ...
  AND o.order_date <= ...;

---

更新:要选择总menu_cost，即菜单上使用的所有库存商品的总成本:

SELECT 
  s.menu_cost,
  ...
FROM  orderlist ol 
INNER JOIN orderdb    o ON ol.order_ID = o.order_ID
INNER JOIN menudb     m ON ol.menu_ID  = m.menu_ID
INNER JOIN recipelist r ON r.menu_ID   = m.menu_ID
INNER JOIN
( 
   SELECT stock_ID, SUM(stock_pricePerPiece) menu_cost
   FROM stocksdb 
   GROUP BY stock_ID
)  s ON r.stock_ID  = s.stock_ID 
WHERE o.order_date >= ...
  AND o.order_date <= ...;