c#，如何使用查询进行搜索

Question

我想做搜索。我使用c#连接MySQL数据库。以及何时创建表之间的实体关系图。我想要使用查询，如查找与移动的客户，这个特定的分配属于特定的客户。

我试试这个。

MySqlConnection connection = new MySqlConnection(MyConnectionString);
connection.Open();

try
{
    MySqlCommand cmd = connection.CreateCommand();


    cmd.CommandText = "SELECT *  FROM assignments  WHERE assignments.Customer_ID = customers.Customer_ID;
    //assignments and customers are tables
    MySqlDataAdapter adap = new MySqlDataAdapter(cmd);
    DataSet ds = new DataSet();
    adap.Fill(ds);
    dataGridView5.DataSource = ds.Tables[0].DefaultView;


}
catch (Exception)
{

    //throw;

    MessageBox.Show("Please complete correct the fields");
}

finally
{

    if (connection.State == ConnectionState.Open)
    {

        connection.Clone();

    }
}

有谁可以帮我？

Answer 1

您的查询似乎是错误的。您需要像这样正确地连接表：

cmd.CommandText = "SELECT *  FROM assignments 
       inner join Customers on assignments.Customer_ID = customers.Customer_ID";

Answer 2

String mobile = "";
using (MySqlConnection conn = new MySqlConnection(mySqlConn)) {
            try
            {
                conn.Open();
                string queryString = "SELECT mobile FROM assignments 
       inner join Customers on assignments.Customer_ID = customers.Customer_ID";
                MySqlCommand cmd = new MySqlCommand(queryString, conn);
                using (MySqlDataReader rdr = cmd.ExecuteReader()) {
                    while (rdr.Read())
                    {
                        mobile = rdr[0].ToString();
                    }
                }
            }
            catch (Exception ex) {  }
        }