您只需要将代码 Package 到一个方法中。下面是一个示例：

public class SqlQuery
{
    private string cs = Environment.GetEnvironmentVariable("SqlConnectionString");

    public void Query()
    {
        using(var conn = new SqlConnection(cs))
        {
            conn.Open();
            var cmd = conn.CreateCommand("SELECT * FROM Table");
            var dr = cmd.ExecuteReader();

            if(dr == null) return;

            while(dr.Read())
            {

            }
        }
    }

}

您共享的屏幕截图包含一个类，并且已经在类中开始实现，而您应该在类中至少创建一个方法，然后将代码添加到返回所需数据的方法中。试着让它起作用！

public class SqlQuery{
public void ExecuteReader()
{
    private string cs =Environment.GetEnvironmentVariable("SqlConnectionString");
    using(var conn = new SqlConnection(cs))
    {
          conn.Open();
          var cmd = conn.CreateCommand("SELECT * FROM Table");
          var dr = cmd.ExecuteReader();
          if(dr == null) return;
          while(dr.Read())
          {

         }
    }
}}