数据库的基本使用（C#语言）

时间 2019-12-04

标签数据库基本使用 c# 语言栏目 SQL 繁體版

原文原文链接

目录sql

数据库的基本使用
@数据库

insert

格式： insert into 表名() values()
其中，values 是带sexpress

**格式： i**nsert into T1(name,age) values('aaa',30)
T1是表名；
name，age 是T1表中的键名，则'aaa',30是分别对应的值  
== >values中的顺序要和表名后的顺序一致。

select 的使用

格式： select Name,Id from T1
Name, Id 是表中的键名，多个键名之间使用逗号分开
T1 是表格

delete

"delete from Table_Student where Name ='aaa' "; 
   
delete from T_Student where Name='yzk'   

从 T_Student表中删除Name字段等于yzk的数据

delete from T_Student  删除全部数据

delete from T_Student where Age>100 or Name='yzk' 或者

delete from T_Student where Age>100 and Height>150  而且

update 更新

update T_Student set Age=Age+1

update T_Student set Age=Age+1,AiHao='吃饭'

update T_Student set AiHao='散步' where Age>100

select * from T_Student where Age<30

Like模糊查询

select * from T_Student where Name like 'y%'    这个是查询以y开头的数据

select * from T_Student where Name like 'y%k'   这个是查询以y开头,  k为结尾的数据


select * from T_Student where Name like '%a%'   查询含有名字中含有a 的数据

Order 排序

按照一个字段排序 select * from T_Student order by Age 默认是升序排列ide

select * from T_Student order by Age, Height

若是Age同样，则再按照Height排序函数

下面是降序排列，降序Descendingspa

select * from T_Student order by Age Desc

下面是若是Age同样，则再按照Height排序.net

select * from T_Student order by Age, Height DEsc

下面的语句是一个总体3d

select * from T_Student where Name like 'y%' 
order by Age

where要在order by以前code

GETDATA()

GETDATA()，sql 内置的函数
用来获取当前时间
其中，下面的as是在查询结果显示的时候，起别名orm

select Name as selectname, GETDATE() from Table_Student

聚合函数：MAX，MIN，AVG，SUM，COUNT

Max

查询Height、Age的最大值
select Max(Height) as maxid, Age as myAge   from Table_Student

COUNT

下面是查询在Age > 100 中全部的行数
select COUTN(*) from Table_Student where Age >100

ADO.Net 平台的使用

简介：.Net中用来向数据库提交执行SQL语句的一堆类。

在C#中使用的格式

// SqlConnection 继承的父类 SqlConnection 实如今对自动回收接口的继承
            // public abstract class DbConnection : Component, IDbConnection, IDisposable
            /* SqlConnection 实例化创建新的链接
             *  Data Source 表示 IP,若是是本机通讯的话，只须要写 .  就能够了
             *  Initial Catalog 对应的数据库中将要操做的表格
             *  User ID 表示数据库登陆的帐户名称，sa表示的是管理员帐户名称
             *  Password 表示数据库登陆的密码
             * 
             */
            // 如数据库创建链接
            using (SqlConnection conn = new SqlConnection
                ("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                
                conn.Open();    // 打开数据库
                /*
                 *  conn.CreateCommand  建立操做命令
                 *  cmd.CommandText     后面接的是sql语句
                 *  cmd.ExecuteNonQuery(); 实施查询
                 *  
                 */

                using (SqlCommand cmd = conn.CreateCommand())  // 建立数据库的操做指令信息
                {
                    // 操做数据库的相关指令信息

                }
            }

insert 在 C# 的使用

一下是在wpf 中的Button按钮对应的控制方法
,cs 文件内容以下：

/// <summary>
        /// 向数据库写入信息
        /// Insert语句的使用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button_Click(object sender, RoutedEventArgs e)
        {
            // SqlConnection 继承的父类 SqlConnection 实如今对自动回收接口的继承
            // public abstract class DbConnection : Component, IDbConnection, IDisposable
            /* SqlConnection 实例化创建新的链接
             *  Data Source 表示 IP,若是是本机通讯的话，只须要写 .  就能够了
             *  Initial Catalog 对应的数据库中将要操做的表格
             *  User ID 表示数据库登陆的帐户名称，sa表示的是管理员帐户名称
             *  Password 表示数据库登陆的密码
             * 
             */
            using (SqlConnection conn = new SqlConnection
                ("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                
                conn.Open();    // 打开数据库的链接
                /*
                 *  conn.CreateCommand  建立操做命令
                 *  cmd.CommandText     后面接的是sql语句
                 *  cmd.ExecuteNonQuery(); 实施查询
                 *  
                 */
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "Insert into Table_Student(Name, Age, Height) Values ('Vs插入数据', 12, 12.1212)";
                    cmd.ExecuteNonQuery();

                }
                MessageBox.Show("写入数据成功");

            }
        }

对应的
MainWindow.xaml文件以下

<Window x:Class="ShuJuKu15_ADONet_JiChu.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ShuJuKu15_ADONet_JiChu"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Button x:Name="button" Content="写入数据" HorizontalAlignment="Left" Margin="230,92,0,0" VerticalAlignment="Top" Width="75" Click="button_Click"/>
   
    </Grid>
</Window>

对应的界面以下

delete 的使用

对应的.cs文件

/// <summary>
        /// 数据库删除信息
        /// delete语句的使用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_delete_Click(object sender, RoutedEventArgs e)
        {
            // SqlConnection 继承的父类 SqlConnection 实如今对自动回收接口的继承
            // public abstract class DbConnection : Component, IDbConnection, IDisposable
            using (SqlConnection conn = new SqlConnection
                ("Data Source = .; Initial Catalog = MyTest; User ID = sa; Password = 123"))
                //("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "delete from Table_Student where Name ='aaa' ";
                    cmd.ExecuteNonQuery();

                }
                MessageBox.Show("删除数据成功");

            }
        }

对应的.wpf文件

<Window x:Class="ShuJuKu15_ADONet_JiChu.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ShuJuKu15_ADONet_JiChu"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Button x:Name="btn_delete" Content="删除数据" HorizontalAlignment="Left" Margin="230,120,0,0" VerticalAlignment="Top" Width="75" Click="btn_delete_Click" />
    </Grid>
</Window>

对应的界面

其余的操做同理。最后，融合在一块儿后，造成的界面以下：

对应的.wpf 文件以下

<Window x:Class="ShuJuKu15_ADONet_JiChu.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ShuJuKu15_ADONet_JiChu"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Button x:Name="button" Content="写入数据" HorizontalAlignment="Left" Margin="230,92,0,0" VerticalAlignment="Top" Width="75" Click="button_Click"/>
        <Button x:Name="btn_delete" Content="删除数据" HorizontalAlignment="Left" Margin="230,120,0,0" VerticalAlignment="Top" Width="75" Click="btn_delete_Click" />
        <Button x:Name="btn_update" Content="更新数据" HorizontalAlignment="Left" Margin="230,150,0,0" VerticalAlignment="Top" Width="75" Click="btn_update_Click" />
        <Button x:Name="btn_queryAllLine" Content="查询总行数" HorizontalAlignment="Left" Margin="363,92,0,0" VerticalAlignment="Top" Width="75" Click="btn_queryAllLine_Click"/>
        <Button x:Name="btn_writeAndReturnId" Content="写入数据并方式对应的ID" HorizontalAlignment="Left" Margin="320,120,0,0" VerticalAlignment="Top" Width="150"  Click="btn_writeAndReturnId_Click"/>
   
    </Grid>
</Window>

对应的.cs文件以下

using System;
using System.Collections.Generic;
using System.Data.SqlClient;    // 数据库空间引入
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace ShuJuKu15_ADONet_JiChu
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        /// <summary>
        /// 向数据库写入信息
        /// Insert语句的使用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button_Click(object sender, RoutedEventArgs e)
        {
            // SqlConnection 继承的父类 SqlConnection 实如今对自动回收接口的继承
            // public abstract class DbConnection : Component, IDbConnection, IDisposable
            /* SqlConnection 实例化创建新的链接
             *  Data Source 表示 IP,若是是本机通讯的话，只须要写 .  就能够了
             *  Initial Catalog 对应的数据库中将要操做的表格
             *  User ID 表示数据库登陆的帐户名称，sa表示的是管理员帐户名称
             *  Password 表示数据库登陆的密码
             * 
             */
            using (SqlConnection conn = new SqlConnection
                ("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                
                conn.Open();    // 打开数据库的链接
                /*
                 *  conn.CreateCommand  建立操做命令
                 *  cmd.CommandText     后面接的是sql语句
                 *  cmd.ExecuteNonQuery(); 实施查询
                 *  
                 */
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "Insert into Table_Student(Name, Age, Height) Values ('Vs插入数据', 12, 12.1212)";
                    cmd.ExecuteNonQuery();

                }
                MessageBox.Show("写入数据成功");

            }
        }

        /// <summary>
        /// 数据库删除信息
        /// delete语句的使用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_delete_Click(object sender, RoutedEventArgs e)
        {
            // SqlConnection 继承的父类 SqlConnection 实如今对自动回收接口的继承
            // public abstract class DbConnection : Component, IDbConnection, IDisposable
            using (SqlConnection conn = new SqlConnection
                ("Data Source = .; Initial Catalog = MyTest; User ID = sa; Password = 123"))
                //("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "delete from Table_Student where Name ='aaa' ";
                    cmd.ExecuteNonQuery();

                }
                MessageBox.Show("删除数据成功");

            }
        }
        /// <summary>
        /// 数据库更新信息
        ///  update 语句的使用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_update_Click(object sender, RoutedEventArgs e)
        {
            using (SqlConnection conn = new SqlConnection
                ("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "update Table_Student set Age = 2 where Name ='Vs插入数据' ";
                    cmd.ExecuteNonQuery();

                }
                MessageBox.Show("更新数据成功");

            }
        }

        /// <summary>
        /// 数据库查询信息
        /// select 语句的应用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_queryAllLine_Click(object sender, RoutedEventArgs e)
        {
            using (SqlConnection conn = new SqlConnection
                ("Data Source  = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                int tmp = 0;
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "select count(*) from Table_Student ";
                    int i = (int)cmd.ExecuteScalar();   //ExecuteScalar通常用来执行有且只有一行一列返回值的SQL语句
                    tmp = i;
                    /*
                    //下面这段是查询数据库表格中是否有'aaa'并返回aaa
                    cmd.CommandText = "select 'aaa'";
                    //ExecuteScalar通常用来执行有且只有一行一列返回值的SQL语句
                    string s = (string)cmd.ExecuteScalar();
                    MessageBox.Show(s);
                    */
                }
                MessageBox.Show("总共有【" + tmp + "】条数据");
            }
        }

        /// <summary>
        /// 写入数据库中的表格并获取ID
        /// insert 与 select ，及关键词 @@identity ， output 的使用
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_writeAndReturnId_Click(object sender, RoutedEventArgs e)
        {
            // SqlConnection 继承的父类 SqlConnection 实如今对自动回收接口的继承
            // public abstract class DbConnection : Component, IDbConnection, IDisposable
            using (SqlConnection conn = new SqlConnection
                ("Data Source = 192.168.43.102; Initial Catalog = MyTest; User ID = sa; Password = 123"))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {

                    cmd.CommandText = "insert into Table_Student(Name, Age) values('bbb', 111)";
                    cmd.CommandText = "select Max(ID) as maxid Table_Student ";
                    string s = (string)cmd.ExecuteScalar();
                    MessageBox.Show(s);
                    //得到自字段的值
                    // @@ 是什么意思
                    // 这段注释一样是写入数据库中的表格并获取ID， 可是不是很好，由于这是，若是下写入数据后，若是有新的数据
                    //忽然插进来写入新的数据，这个时候获取的ID就不是原来的ID ， 而是新的ID，这就不对了
                    cmd.CommandText = "insert into Table_Student(Name,Age) values('aaa',123) ;select @@identity";
                    decimal i = (decimal)cmd.ExecuteScalar();//

                    ////写入数据并返回该数据对应的id值
                    //cmd.CommandText = "insert into Table_Student(Name,Age) output inserted.Id values('aaa',123) ";
                    //long i = (long)cmd.ExecuteScalar();//数据库bigint→C#平台long
                    MessageBox.Show(i.ToString());
                }
                MessageBox.Show("写入数据成功");

            }
        }
    }
}