c#-sql之having

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

using System.Data.SqlClient;

namespace UseHaving

{

    public partial class Frm_Main : Form

    {

        public Frm_Main()

        {

            InitializeComponent();

        }

        private void Frm_Main_Load(object sender, EventArgs e)

        {

            dgv_Message.DataSource = GetMessage();//设置数据源

        }

        private void btn_Select_Click(object sender, EventArgs e)

        {

            dgv_Message.DataSource = GetGrade();//设置数据源

        }

        /// <summary>

        /// 查询数据库信息

        /// </summary>

        /// <returns>方法返回DataTable对象</returns>

        private DataTable GetGrade()

        {

            string P_Str_ConnectionStr = string.Format(//创建数据库连接字符串

                @"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\DataBase\db_TomeTwo.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

            string P_Str_SqlStr = string.Format(//创建SQL查询字符串

                @"SELECT 所在学院,COUNT(*) AS 人数,MAX(高数) AS 最高成绩,AVG(高数) AS 高数平均成绩

FROM

tb_student AS st

JOIN tb_grade AS gr

ON

st.学生编号 = gr.学生编号

GROUP BY 所在学院

HAVING AVG(高数) > 60");

            SqlDataAdapter P_SqlDataAdapter = new SqlDataAdapter(//创建数据适配器

                P_Str_SqlStr, P_Str_ConnectionStr);

            DataTable P_dt = new DataTable();//创建数据表

            P_SqlDataAdapter.Fill(P_dt);//填充数据表

            return P_dt;//返回数据表

        }

        /// <summary>

        /// 查询数据库信息

        /// </summary>

        /// <returns>方法返回DataTable对象</returns>

        private DataTable GetMessage()

        {

            string P_Str_ConnectionStr = string.Format(//创建数据库连接字符串

                @"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\DataBase\db_TomeTwo.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

            string P_Str_SqlStr = string.Format(//创建SQL查询字符串

                "SELECT * FROM tb_Student");

            SqlDataAdapter P_SqlDataAdapter = new SqlDataAdapter(//创建数据适配器

                P_Str_SqlStr, P_Str_ConnectionStr);

            DataTable P_dt = new DataTable();//创建数据表

            P_SqlDataAdapter.Fill(P_dt);//填充数据表

            return P_dt;//返回数据表

        }

    }

}