C# OleDb参数,空值
我有以下代码C# OleDb参数,空值,c#,.net,oledb,C#,.net,Oledb,我有以下代码 OleDbCommand cmd = new OleDbCommand("SELECT * FROM Users WHERE username = ? AND password = ?",conn); OleDbParameter p1 = new OleDbParameter(); OleDbParameter p2 = new OleDbParameter(); cmd.Parameters.Add(p1); cmd.Parameter
OleDbCommand cmd = new OleDbCommand("SELECT * FROM Users WHERE username = ? AND password = ?",conn);
OleDbParameter p1 = new OleDbParameter();
OleDbParameter p2 = new OleDbParameter();
cmd.Parameters.Add(p1);
cmd.Parameters.Add(p2);
p1.Value = usernametb.Text;
p2.Value = passwordtb.Text;
conn.Open();
OleDbDataReader read = cmd.ExecuteReader();
if (read.Read() == true)
{
conn.Close();
MessageBox.Show("Successfully logged in!");
}
else
{
conn.Close();
MessageBox.Show("Login failed");
}
如果用户有密码,此代码对我有效,但如果用户没有密码,则会失败,我不知道原因
我哪里出了问题?下面的步骤行吗
SELECT * FROM Users WHERE username = ? AND
(password IS NULL OR password = ?)
这是因为在SQL标准中,返回的是
null=null
而不是true
您的查询应该是
SELECT * FROM Users WHERE username = ? AND (password is null or password = ?)
更好的查询方法是检查当密码为null
时,用户必须输入一个空密码,因此密码如下:
SELECT * FROM Users WHERE username = ? AND
? = case when password is null then '' else password end
您从何处获得错误以及问题是什么。?::)我猜这里
p2.Value=passwordtb.Text代码>错误为对象引用。。。对的