如何从数据库中获取值?必须声明标量变量"@ID1"
本文关键字:quot 声明 标量 变量 @ID1 数据库 获取 | 更新日期: 2023-09-27 18:16:37
public partial class Form3 : Form
{
string var;
int ID1;
private void button1_Click(object sender, EventArgs e)
{
ID1 = int.Parse(textBox1.Text);
SqlConnection cn = new SqlConnection(@"Data Source=.'SQLEXPRESS;AttachDbFilename=C:'Users'asp'Desktop'DatabasesPractice'DatabasesPractice'soccer.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
SqlCommand dataCommand = new SqlCommand("SELECT Name FROM team WHERE ID = @ID1", cn);
cn.Open();
var = Convert.ToString(dataCommand.ExecuteScalar());
label3.Text = var;
}
}
它给了我一个错误,说我必须声明标量变量@ID
,我到处搜索,不能得到我的具体情况的解决方案。
谢谢大家的帮助!D
public partial class Form3 : Form
{
string var;
int ID1;
private void button1_Click(object sender, EventArgs e)
{
ID1 = int.Parse(textBox1.Text);
SqlConnection cn = new SqlConnection(@"Data Source=.'SQLEXPRESS;AttachDbFilename=C:'Users'asp'Desktop'DatabasesPractice'DatabasesPractice'soccer.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
SqlCommand dataCommand = new SqlCommand("SELECT Name FROM team WHERE ID = @ID1", cn);
dataCommand.Parameters.AddWithValue("@ID1", ID1); // this is the new line of code
cn.Open();
var = Convert.ToString(dataCommand.ExecuteScalar());
label3.Text = var;
}
}
见上文,我添加了dataCommand.Parameters.AddWithValue("@ID1", ID1);
。它所做的是为SQL查询定义参数并将值传递给它。我假设您希望变量ID1
作为SQL参数@ID1
的值。
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.aspx
SqlCommand
有一个Parameters
集合。
参见:http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.parameters.aspx
:
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(commandText, connection);
command.Parameters.Add("@ID", SqlDbType.Int);
command.Parameters["@ID"].Value = customerID;
// Use AddWithValue to assign Demographics.
// SQL Server will implicitly convert strings into XML.
command.Parameters.AddWithValue("@demographics", demoXml);
try
{
connection.Open();
Int32 rowsAffected = command.ExecuteNonQuery();
Console.WriteLine("RowsAffected: {0}", rowsAffected);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
您需要传入参数的值。在初始化dataccommand变量之后添加这一行:
dataCommand.Parameters.Add("@ID", ID1);
您需要为dataccommand添加一个参数,因为您说有一个。
ID = @ID1
告诉服务器从参数@ID1获取数据。那么就不用声明形参了。
检查dataccommand对象的Parameters收集。添加参数
您必须将Parameter添加到SqlCommand.Parameters
集合中,因为您在查询中设置@ID1
在ExecuteScalar
dataCommand.Parameters.Add(new SqlParameter("@ID1", ID1));
的完整解决方案public partial class Form3 : Form
{
string var;
int ID1;
private void button1_Click(object sender, EventArgs e)
{
ID1 = int.Parse(textBox1.Text);
SqlConnection cn = new SqlConnection(@"Data Source=.'SQLEXPRESS;AttachDbFilename=C:'Users'asp'Desktop'DatabasesPractice'DatabasesPractice'soccer.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
SqlCommand dataCommand = new SqlCommand("SELECT Name FROM team WHERE ID = @ID1", cn);
dataCommand.Parameters.Add(new SqlParameter("@ID1", ID1));
cn.Open();
var = Convert.ToString(dataCommand.ExecuteScalar());
label3.Text = var;
}
}
希望对您有所帮助