mysqlnull.aspx.cs

ASP C#代码实例 适合初学人士学习使用

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using System.Configuration;

namespace Example_7_10
{
	/// <summary>
	/// Summary description for MySQLNULL.
	/// </summary>
	public class MySQLNULL : System.Web.UI.Page
	{
		protected System.Web.UI.WebControls.Label TureNULL;
		protected System.Web.UI.WebControls.Label FalseNULL;
		protected System.Web.UI.WebControls.Label NULLTrue;
		protected System.Web.UI.WebControls.Label NullFalse;
		protected System.Web.UI.WebControls.Label NULLNULL;
		protected System.Web.UI.WebControls.Button GetNULLValue;
		private readonly string SQLCONNECTIONSTRING = ConfigurationSettings.AppSettings["SQLCONNECTIONSTRING"].ToString();

		private void Page_Load(object sender, System.EventArgs e)
		{
			if(!Page.IsPostBack)
			{
				///初始化布尔运算的表达式
				SetNULL();
			}
		}

		private void SetNULL()
		{
			TureNULL.Text  = "True AND NULL";
			FalseNULL.Text = "False AND NULL";
			NullFalse.Text = "NULL AND False";
			NULLTrue.Text  = "NULL AND True";
			NULLNULL.Text  = "NULL AND NULL";
		}

		private void CalNULLValue()
		{
			TureNULL.Text  = GetNULLValues(TureNULL.Text);
			FalseNULL.Text = GetNULLValues(FalseNULL.Text);
			NullFalse.Text = GetNULLValues(NullFalse.Text);
			NULLTrue.Text  = GetNULLValues(NULLTrue.Text);
			NULLNULL.Text  = GetNULLValues(NULLNULL.Text);		
		}

		private string GetNULLValues(string nullString)
		{
			String nullValue = "";

			switch(nullString)
			{
				case "True AND NULL":
				{
					nullString = "(1=1) AND (1=NULL)";
					break;
				}
				case "False AND NULL":
				{
					nullString = "(1=0) AND (1=NULL)";
					break;
				}
				case "NULL AND False":
				{
					nullString = "(1=NULL) AND (1=0)";
					break;
				}
				case "NULL AND True":
				{
					nullString = "(1=NULL) AND (1=1)";
					break;
				}
				case "NULL AND NULL":
				{
					nullString = "(1=NULL) AND (1=NULL)";
					break;
				}
				default:break;
			}

			///从数据库中Tabs表获取所有记录
			String cmdText = "SELECT NULLValue = (CASE WHEN " + nullString + " THEN 'True' ELSE 'FALSE' END)";
			SqlConnection myConnection = new SqlConnection(SQLCONNECTIONSTRING);
			SqlCommand myCommand = new SqlCommand(cmdText,myConnection);

			///执行数据库查询
			myConnection.Open();
			SqlDataReader dr = myCommand.ExecuteReader();

			if(dr.Read())
			{
				nullValue = dr["NULLValue"].ToString();
			}			
		
			///关闭读取器和数据库的链接
			dr.Close();
			myConnection.Close();

			return(nullValue);
		}

		#region Web Form Designer generated code
		override protected void OnInit(EventArgs e)
		{
			//
			// CODEGEN: This call is required by the ASP.NET Web Form Designer.
			//
			InitializeComponent();
			base.OnInit(e);
		}
		
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{    
			this.GetNULLValue.Click += new System.EventHandler(this.GetNULLValue_Click);
			this.Load += new System.EventHandler(this.Page_Load);

		}
		#endregion		

		private void GetNULLValue_Click(object sender, System.EventArgs e)
		{
			CalNULLValue();
			GetNULLValue.Enabled = false;
		}
	}
}