c# - 如何从 mysql 查询中存储对象 max(date) 和 min(date)

Question

我是 C# 的半新手，我从未存储过来自 mysql 查询的对象。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最大(日期)和最小(日期)

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';";

比如: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';";
    }

有人可以告诉我应该写什么样的代码行吗？也许 cmd.Parameters 就足够了？感谢您的帮助。

这是我的代码:

 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

您可以使用 ExecuteReader检索值如下，

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]);
       }
    }
}
}

希望对您有所帮助。