Question

c# 连接access时出现 未处理oledbexception 错误

mycon.Open();

string sql1 = "select username from login where username = '" + textBox1.Text.Trim() + "',password='" + textBox2.Text.Trim() + "'";
OleDbCommand cmd = new OleDbCommand("", mycon);
cmd.CommandText = sql1;
if (null == cmd.ExecuteScalar())
{
string sql2 = "insert into login (username,password)" + " values ('" + textBox1.Text.Trim() + "','" + textBox2.Text.Trim() + "')";
cmd.CommandText = sql2;
cmd.ExecuteNonQuery();
MessageBox.Show("添加用户成功！", "提示");

Answer 1

OleDbCommand cmd = new OleDbCommand("", mycon)这句改为：
OleDbCommand cmd = new OleDbCommand(sql1, mycon).
sql1语句中的username = '" + textBox1.Text.Trim() + "',password='" + textBox2.Text.Trim() + "'";
改为username = '" + textBox1.Text.Trim() + "' and password='" + textBox2.Text.Trim() + "'";

Answer 2

string sql1 = "select username from login where username = '" + textBox1.Text.Trim() + "',password='" + textBox2.Text.Trim() + "'";

password前多了个逗号吧应该是and

Answer 3

string sql1 = "select username from login where username = '" + textBox1.Text.Trim() + "' and password='" + textBox2.Text.Trim() + "'";

Answer 4

估计是OleDbCommand cmd = new OleDbCommand("", mycon)这句出错。
初始化OleDbCommand时给空字符串可能出现异常.
试试改为：
OleDbCommand cmd = new OleDbCommand()；
cmd.Connection=mycon;
cmd.CommandText = sql1;