如何从mysql查询中存储对象max（date）和min（date）

Question

我是C＃的半新手，我从不存储mysql查询中的对象。我已经声明了2个Datetimes变量：

DateTime date_min
DateTime date_max

我想从下面的查询中存储max（date）和min（date）

string query1 = "SELECT MIN(order_status.BEGIN_DATE) AS 'BEGIN DATE', MAX(order_status.END_DATE) AS 'END DATE' FROM project1.order_status INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER WHERE orders.NUMBER_ORDER = 'TEST';";

像：max(date) = MAX(order_status.END_DATE)

min(date) = MIN(order_status.BEGIN_DATE)

我想在这个循环中使用：

    for (DateTime date = date_min; date <= date_max; date = date.AddDays(1))
    {             
        string query2 = "SELECT COUNT(leave.ID_PRACOWNIKA) AS 'NUMBER OF WORKERS ON LEAVE' FROM project1.leave WHERE DATE(leave.BEGIN_DATE) <= '"+date+"' AND DATE(leave.END_DATE) >= '"+date+"';";
        string query3 = "SELECT TIME_FORMAT(SEC_TO_TIME(SUM(TIME_TO_SEC(order_status.END_DATE) - TIME_TO_SEC(order_status.BEGIN_DATE))), '%H:%i:%s') AS 'TIME OF ALL ORDERS IN DAY' FROM project1.order_status INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER WHERE (DATE(order_status.BEGIN_DATE) = '"+date+"' AND DATE(order_status.END_DATE) = '"+date+"');";
        string query4 = "SELECT TIME_FORMAT(SEC_TO_TIME(SUM(TIME_TO_SEC(order_status.END_DATE) - TIME_TO_SEC(order_status.BEGIN_DATE))), '%H:%i:%s') AS 'TIME OF ORDER IN DAY' FROM project1.order_status INNER JOIN project1.orders ON orders.ID_ORDER  = order_status.ID_ORDER WHERE (DATE(order_status.BEGIN_DATE) = '"+date+"' AND DATE(order_status.END_DATE) = '"+date+"') AND orders.NUMBER_ORDER = 'TEST';";
    }

有人可以说明我应该写什么样的代码行吗？也许cmd.Parameters就够了？ THX任何帮助。

有我的代码：

 public partial class GenerateChartsOfOrders : Form
    {
        DateTime date_min;
        DateTime date_max;
        public GenerateChartsOfOrders()
        {
            InitializeComponent();
        }
        public void loaddata2()
        {
string query1 = "SELECT MIN(order_status.BEGIN_DATE) AS 'BEGIN DATE', MAX(order_status.END_DATE) AS 'END DATE' FROM project1.order_status INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER WHERE orders.NUMBER_ORDER = 'TEST';";

            for (DateTime date = date_min; date <= date_max; date = date.AddDays(1))
            {             
                string query2 = "SELECT COUNT(leave.ID_PRACOWNIKA) AS 'NUMBER OF WORKERS ON LEAVE' FROM project1.leave WHERE DATE(leave.BEGIN_DATE) <= '"+date+"' AND DATE(leave.END_DATE) >= '"+date+"';";
                string query3 = "SELECT TIME_FORMAT(SEC_TO_TIME(SUM(TIME_TO_SEC(order_status.END_DATE) - TIME_TO_SEC(order_status.BEGIN_DATE))), '%H:%i:%s') AS 'TIME OF ALL ORDERS IN DAY' FROM project1.order_status INNER JOIN project1.orders ON orders.ID_ORDER = order_status.ID_ORDER WHERE (DATE(order_status.BEGIN_DATE) = '"+date+"' AND DATE(order_status.END_DATE) = '"+date+"');";
                string query4 = "SELECT TIME_FORMAT(SEC_TO_TIME(SUM(TIME_TO_SEC(order_status.END_DATE) - TIME_TO_SEC(order_status.BEGIN_DATE))), '%H:%i:%s') AS 'TIME OF ORDER IN DAY' FROM project1.order_status INNER JOIN project1.orders ON orders.ID_ORDER  = order_status.ID_ORDER WHERE (DATE(order_status.BEGIN_DATE) = '"+date+"' AND DATE(order_status.END_DATE) = '"+date+"') AND orders.NUMBER_ORDER = 'TEST';";
            }
        }
    }

Answer 1

你可以使用ExecuteReader来检索下面的值，

using (MySqlConnection connection = new MySqlConnection(connectionString))
{
using(var command = new MySqlCommand(query1, con))
{
    using(var reader = command.ExecuteReader())
    {
       while (reader.Read())
       {
        date_min = Convert.ToDateTime(reader[0]);
        date_max = Convert.ToDateTime(reader[1]);
       }
    }
}
}

希望能帮助到你。