c# - 只打印数据库第一行的数据而不是整个表

Question

我需要输出仅在第一行的数据，但它正在打印添加到数据库表中的所有数据。这是数据:

例如，它应该只打印“Not Very Nice”和 ID 为 27 的消息，而不是 ID 为 28 的第二行。

代码如下:

using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;

public partial class feedback1 : System.Web.UI.Page
{
    SqlConnection con;
    string cons = ConfigurationManager.ConnectionStrings["constring"].ConnectionString;
    SqlCommand cmd;
        protected void Page_Load(object sender, EventArgs e)
    {

    }
        protected void Button1_Click(object sender, EventArgs e)
        {
            con = new SqlConnection(cons);
            con.Open();
            cmd = new SqlCommand("insert into feedback(username,message) values('" + TextBox1.Text + "','" + TextBox2.Text +"')", con);
            cmd.ExecuteNonQuery();
        }
}

这是输出..

这是输出页面代码..

 <form id="form1" runat="server">
         <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="id" DataSourceID="SqlDataSource1" EnableModelValidation="True" OnSelectedIndexChanged="GridView1_SelectedIndexChanged" GridLines="None">
        <Columns>
            <asp:BoundField DataField="id" InsertVisible="False" ReadOnly="True" SortExpression="id" />
            <asp:BoundField DataField="username" HeaderText="username" SortExpression="username" />
            <asp:BoundField DataField="message" HeaderText="message" SortExpression="message" />
        </Columns>
    </asp:GridView>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" OnSelecting="SqlDataSource1_Selecting" SelectCommand="SELECT * FROM [feedback]"></asp:SqlDataSource>
    <div>

    </div>
    </form>

Answer 1

这只是修改 SQL 查询的一个例子:

选择第一行:

<asp:SqlDataSource 
    ID="SqlDataSource1" 
    runat="server" 
    ConnectionString="<%$ ConnectionStrings:ConnectionString %>" 
    OnSelecting="SqlDataSource1_Selecting" 
    SelectCommand="SELECT * FROM [feedback] LIMIT 1">
</asp:SqlDataSource>

选择特定的 ID:

<asp:SqlDataSource 
    ID="SqlDataSource1" 
    runat="server" 
    ConnectionString="<%$ ConnectionStrings:ConnectionString %>" 
    OnSelecting="SqlDataSource1_Selecting" 
    SelectCommand="SELECT * FROM [feedback] WHERE [id] = REPLACE_WITH_YOUR_NUMBER">
</asp:SqlDataSource>

"Note: Not all database systems support the SELECT TOP clause. MySQL supports the LIMIT clause to select a limited number of records."

请参阅:https://www.w3schools.com/sql/sql_top.asp

注意

您的程序容易受到 SQL 注入(inject)攻击。 请修改您的输入以在执行之前清理您的查询。

protected void Button1_Click(object sender, EventArgs e)
{
    con = new SqlConnection(cons);
    con.Open();
    string txtb1= TextBox1.Text,
           txtb2= TextBox2.Text;
    sqlCommand.CommandText = "select * from product where name = @name";
    cmd = new SqlCommand("insert into feedback(username,message) values('" + @txtb1 + "','" + @txtb2 +"')", con);
    cmd.Parameters.AddWithValue("txtb1", txtb1);
    cmd.Parameters.AddWithValue("txtb2", txtb2);
    cmd.ExecuteNonQuery();
}

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