Question

string sql = "select * from customer where name like '" + textBox2.Text + "%'";
string sql2 = "select * from customer";

if (textBox2.Text.Length > 0)
{
    DataTable dt = CarDatabase.executeSelect(sql);
    DataTable dt2 = CarDatabase.executeSelect(sql2);

    if (dt == null)
    {
        dataGridView2.DataSource = dt2;
        MessageBox.Show("There's no result with " + textBox2.Text);
    }
    else if (dt != null)
        dataGridView2.DataSource = dt;
}
else
{
    MessageBox.Show("Please fill the textbox");
}

我尝试“如果like有一些结果，请在DataGrid”中显示。没问题。但是，当like在数据库中找不到任何内容时，DataGrid会保持旧状态。但是，如果在搜索后没有结果，则DataGrid为空。

Answer 1

string sql = "select * from customer where name like '" + textBox2.Text + "%'";
string sql2 = "select * from customer";

if (textBox2.Text.Length > 0)
{
    DataTable dt = CarDatabase.executeSelect(sql);
    DataTable dt2 = CarDatabase.executeSelect(sql2);

    if (dt == null)
    {
        dataGridView2.DataSource = dt2;
        dataGridView2.DataBind();
        MessageBox.Show("There's no result with " + textBox2.Text);
    }
    else if (dt != null)
    {
        dataGridView2.DataSource = dt;
        dataGridView2.DataBind();
    }
}
else
{
    MessageBox.Show("Please fill the textbox");
}

Answer 2

使用存储过程比从代码中注入sql查询更好。

我会创建一个像这样的程序......

Create Procedure GetCustomers(@name varchar(100))
AS 
BEGIN
 select * from customer  where Name like (ISNULL(@name,Name))
END

但是，在将值传递给@name参数时，您需要向其追加'％'。如果textbox值为空，则将null传递给@name。如果文本框值为空，则此查询将返回所有客户，否则将返回所请求的客户。

Answer 3

您必须使用DataBind()

在if else块中执行以下行

dataGridView2.DataBind();

更新：

           if (dt == null)
            {
                DataTable table = new DataTable();
                dataGridView2.DataSource = table ;
                MessageBox.Show("There's no result with " + textBox2.Text);
            }

else数据表的声明

3 个答案: