VS实现销售系统查询

Question

```c#
private void button5_Click(object sender, EventArgs e)
        {
            if (textBox2.Text == "" && textBox3.Text == "")
            {
                MessageBox.Show("对不起，请输入价格范围");
                textBox2.Focus();
                return;
            }
                        
            if (textBox2.Text != "" && textBox3.Text == "")
                strSql = "Select Price * From BasicInformationAboutCars where Price  >=  textBox2.text";
            else if(textBox2.Text== "" && textBox3.Text != "")
                strSql = "Select Price * From BasicInformationAboutCars where Price<= + textBox3.Text + ";
            else
                strSql = "Select Price * From BasicInformationAboutCars where Price>= + textBox2.Text + and Price<= + textBox3.Text + ";
            
            exeSQL(strSql);
        }

问题：在textbox2、3中输入数字范围，查询结果不显示？报错：至少一个参数没有被指定值怎么回事？

Answer 1

根据您提供的代码，报错信息"至少一个参数没有被指定值"是由于您在SQL语句中没有正确地引用文本框的值。在SQL语句中，您需要使用字符串拼接的方式将文本框中的值与SQL语句连接起来。

以下是修改后的代码示例：

private void button5_Click(object sender, EventArgs e)
{
    if (textBox2.Text == "" && textBox3.Text == "")
    {
        MessageBox.Show("对不起，请输入价格范围");
        textBox2.Focus();
        return;
    }

    if (textBox2.Text != "" && textBox3.Text == "")
        strSql = "Select Price * From BasicInformationAboutCars where Price >= " + textBox2.Text;
    else if (textBox2.Text == "" && textBox3.Text != "")
        strSql = "Select Price * From BasicInformationAboutCars where Price <= " + textBox3.Text;
    else
        strSql = "Select Price * From BasicInformationAboutCars where Price >= " + textBox2.Text + " and Price <= " + textBox3.Text;

    exeSQL(strSql);
}

在修改后的代码中，使用了字符串拼接的方式将文本框的值与SQL语句连接起来，以正确地传递参数值给SQL查询语句。