c#-sql之having

来源：互联网发布：阿里云专线编辑：程序博客网时间：2024/06/09 19:33

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
        }

}
}

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